
Class - P V 
Bobk__iH_Z4 






GqEyiigMN?- 



CJQPXBIGIIT DEPQSfli 



Digitized by the Internet Archive 
in 2011 with funding from 
The Library of Congress 



http://www.archive.org/details/elementsofscientOOdunl 



THE ELEMENTS OF SCIENTIFIC PSYCHOLOGY 



THE ELEMENTS 

OF 

SCIENTIFIC PSYCHOLOGY 



BY 



KNIGHT DUNLAP 

PROFESSOR OF EXPERIMENTAL PSYCHOLOGY IN THE JOHNS HOPKINS UNIVERSITY, 
BALTIMORE; AUTHOR OF "MYSTICISM, FREUDIANISM AND SCIENTIFIC 
PSYCHOLOGY," "PERSONAL BEAUTY AND RACIAL BETTERMENT," ETC. 



ILLUSTRATED 



ST. LOUIS 

C. V. MOSBY COMPANY 

1922 



"Sic 



Copyright, 1922, by The C. V. Mosby Company 
(All rights reserved) 



Printed in U. S. A. 



SEP 29*22 

©CI.A683464 
o f 



Press of 

The C. V. Mosoy Company 

St. Louis 



TO 



EDWARD P. HYDE, PERCY W. COBB, and 
ARCHIE G. WORTHING 

OF THE NELA RESEARCH LABORATORIES : REPRESENTATIVES OF A GROUP OF MEN 

WHO HAVE BRILLIANTLY ILLUSTRATED THE PRACTICAL VALUE OF 

FOSTERING RESEARCH IN PURE SCIENCE 



PREFACE 



In introducing the student to the modern science of psychol- 
ogy, it is necessary to depart definitely from traditional formulae 
and traditional conceptions in so far as these formulae and con- 
ceptions no longer represent the facts with which psychology has 
to deal. The psychology of today is a science of the conscious re- 
sponses of the organism, and as such is called upon to furnish ma- 
terials applicable to the problems of physical science, education, 
industry and the arts ; and to social problems. Psychology is called 
upon for these contributions, and is responding: but it is only the 
modern form of psychology which can contribute effectively. No 
one thinks today of asking aid in any problem of real life from the 
psychology, however named, which deals with a peculiar world of 
psychic objects, by the introspective method, or by any of its later 
substitutes. One turns instead to the scientific psychology whose 
subject matter is the world of real objects and real activities, 
and whose methods are those of all science. It is impossible to put 
this new wine in the old bottles of phrase and viewpoint which 
sufficed for its predecessor. 

It is necessary, on the other hand, to conserve a large part of 
the psychological results of the past centuries. Scientific psychol- 
ogy is no new invention, but is a legitimate development from the 
older psychology which it cannot avoid supplanting, and as such it 
embodies the achievements of the psychologists from Aristotle to 
the present generation. "With "new psychologies" and with re- 
volts against the essential facts of psychology, scientific psychol- 
ogy has no affiliation, although it represents real progress, and al- 
though its postulates in regard to consciousness differ essentially 
from those of the past. 

This book, being designed for the specific purpose of intro- 
ducing the student to the elements of psychology, and giving him 
a firm ground on which to build, deals with the general problems 
of psychology only. The special topics of learning; of child, ani- 
mal, social and abnormal psychology; of sleep and dreams; and 



8 PREFACE 

of applications to education and the arts and industries, are pur- 
posely omitted. The student, having mastered the course outlined 
in this volume, should have available a volume, or a series of vol- 
umes, prepared by specialists in these topics, and presenting them 
from the scientific point of view. No such volume or series ex- 
ists at present, but we may well expect it in the near future. 

The first chapter of this volume is difficult for beginners, and 
it is possible that instructors will do well to present its most im- 
portant points in simpler form, and have the students begin their 
reading with the second chapter. In that case, the students should 
later return to the first chapter and study it carefully, since it con- 
tains the essential scheme of scientific psychology. 

The ninth chapter is not intended to be an adequate pres- 
entation of the anatomical and physiological facts with which 
the student should be familiar, but as a resume of what the instruc- 
tor should present in greater detail, employing such texts, slides, 
charts and preparations as may be available. It is not possible to 
include in a textbook of psychology the portions of physics and 
the biological sciences required for an adequate study of the sub- 
ject; and such fragmentary details as might be included are not 
sufficient. 

While written primarily for college students, the book is also 
designed to be of assistance to men in various professions who 
wish to become conversant with the foundations of modern psy- 
chology. For the book, while dealing with foundations and not 
with applications, does represent the general point of view on 
which rests the psychology which is being applied in the fields of 
education, industry, and the arts, and which will undoubtedly be 
applied to medicine before long. 

A number of the cuts are from new drawings by Olive C. 
Slater, for whose intelligent and careful work my thanks are heart- 
ily rendered. So many persons have helped me by criticism and 
suggestions and by reading manuscript and proof that I shall not 
enter here the long list of their names, although I am profoundly 
grateful for the assistance each has rendered. 

Knight Dunlap. 

The Johns Hopkins University, 
March 7, 1922. 



TABLE OF CONTENTS 



CHAPTER I 

Introduction 15 

The divisions of psychology, 15 ; The nature of psychology, 19 ; Introspection 
and external observation, 27 ; The methods of psychology, 28 ; Genetic and 
introspectionalist psychology, 33. 

CHAPTER II 

Sense Perception 37 

Complex and elementary sense objects, 37; The characters of sense data, 39; 
The senses, 40; Sensory stimuli, 43; The physiological sensory mechanism, 47. 

CHAPTER III 

The Cranial Senses 50 

Gustation, 50; Olfaction, 53; Vision, 56; Audition, 80. 

CHAPTER IV 

The Somatic, Visceral and Labyrinthine Senses 94 

The dermal senses, 94; Palmesthesis, 99; The sexual sense, 101; Kinesthesis, 
101 ; Bodily feelings, 102. 

CHAPTER V 

Some Details Concerning Sensory Characters 112 

' The relativity of sense data, 112; Stimulus thresholds 113; Physiological con- 
ditions of intensity and quality, 115; Temporal and spatial characters, 117; 
Movement, 119. 

CHAPTER VI 

Some Simple Relations of Sense Data 121 

Relations as objects of consciousness, 121; Identity and difference of sense 
data, 124; Threshold differences of sense data, 124; The intensity difference 
threshold and Weber 's law, 125 ; Intermediacy or betweenness, 129. 

CHAPTER VII 

Some Sensory Measurements 131 

Measurements and tests, 131; Olfactory and gustatory measurements, 132; 
Visual measurements, 135; Auditory measurements, 148; Measurements of 
dermal sensitivity, 151. 

9 



10 CONTENTS 

CHAPTER VIII 



/ 



Thought and Thought Content 156 

Imagination and perception, 156; Reproductive and productive imagination, 
158; Memory and anticipation, 160; Images, ideas and concepts, 162; Sym- 
bolic thinking, 164; The determination of imaginative types, 164; The culti- 
vation of imagination, 168. 

CHAPTER IX 

The Bodily Mechanism 170 

The complex organism a social group, 170; The living cell, 172; The neuron, 
176; Epithelial receptors, 179; The divisions of the nervous system, 179; 
Heredity, 185 ; Reactions and reaction arcs, 186 ; Types of reaction, 189 ; Local 
and spontaneous activities, 198; Mixed reactions, 198; Reactions of the glands 
and smooth muscles, 199. 

CHAPTER X 

Reaction and Consciousness 202 

Degrees of consciousness, 202; Integration, 203. 

CHAPTER XI 

Instinct and Habit 209 

General distinctions, 209; Drainage and habit formation, 210; Instinctive 
reactions and instincts, 214; Consciousness and volition in instinctive reac- 
tions, 219; General principle of habit formation, 223; Specific problems of 
learning, 230. 

CHAPTER XII 

The Development of Perception 238 

Direct and indirect perception, 238; Discrimination, 244; Illusion, 246; The 
conditions of accurate perception, 252; Meaning and symbolic perception, 254. 

CHAPTER XIII 

Space Perception 260 

Space perception and muscular activity, 260; Visual depth perception, 263; 
Non-symbolic factors in space perception, 276; Auditory space perception, 
277; Space perception through other senses, 280; The perception of movement, 
282; Equilibration, 287; Visual anesthesia and perception, 288; Spatial illu- 
sions, 291. 

CHAPTER XIV 

The Thinking Process 298 

The thought reaction, 298; The association of ideas, 304; Mediate associa- 
tions, 306; Formation of automatisms, 307; Reasoning, 307. / 



CONTENTS 11 

CHAPTER XV 

Affective Experience 312 

Feeling and emotion, 312; The nature of feeling, 312; Feeling and reaction, 
314; The simple feelings, 315; Emotions, moods and sentiments, 318; The 
driving force of feelings, 321 ; Desire or cornation, 323 ; Hedonic feeling, 329 ; 
Observational and experimental work on feeling, 331; Feeling and habit, 337. 

CHAPTER XVI 
The Empirical Self or "Me " .... , 340 

APPENDIX I 

Mental Deficiency and Mental Disease 345 

Abnormal psychology and mental inefficiency, 345; The psychoses, 348; The 
Neuroses, 353; Amentia, or mental deficiency, 356. 

APPENDIX II 
Some Useful Reference Books 360 



ILLUSTRATIONS 



FIG- PAGE 

1. Taste tetrahedron 51 

2. Color triangle 59 

3. Color hexahedron 61 

4. Wave motion in the ether 63 

5. Scheme of spectrum production . 61 

6. Diagram of a typical prismatic spectrum of sunlight 65 

7. Color sensitivity of the normal eye 67 

8. Color sensitivity of the dichromatic eye 77 

9. Wave form of pure tone 81 

JO. The wave form of an organ-pipe tone (reedless oboe, middle C, 260 v. s.), with 

its harmonic partials 83 

11. Scheme of a complex tone 91 

12. Scheme of reaction pathways commencing in retinal receptors 182 

13. Scheme of reaction pathways terminating in muscles producing finger movement 183 
34. Scheme of pathways involved in the knee jerk, and in the accompanying per- 
ceptual reactions 191 

15. Practice curve for adding machine 232 

16. Typical pathways covered by a rat in a maze on successive trials in learning 

to reach food in the center 236 

17. Scheme of the pathways and interconnections involved in the development of 

the perception of an orange 241 

18. Hidden figures. An illustration of the effects of previous reactions in deter- 

mining the indirect factors in perception 243 

19. Shadows as signs of depth 270 

20. Linear perspective 27] 

21. Angular perspective, foreshortening and intervention 273 

22. Aerial perspective 274 

23. Aerial perspective 275 

24. Direction of eye movements in horizontal nystagmus 285 

25. Poggendorf 's figure 292 

26. Zollner's figure 293 

27. Reversible perspective figures 294 

28. Jastrow's figure 295 

29. Muller-Lyer 's figure 296 

30. Dunlap's figure 296 

31. Scheme of the pathways involved in the learning of a series of nonsense 

syllables 305 

13 



THE ELEMENTS OF SCIENTIFIC 
PSYCHOLOGY 



CHAPTER I 
INTRODUCTION 

§1. The divisions of psychology. 

It is convenient to divide the field of Psychology into four main 
parts: (1) Adult Human Psychology, (2) Child Psychology, (3) 
Animal Psychology, (4) Social Psychology. The first and second 
parts can each be divided again into, (a) Normal Psychology, and 
(b) Pathological or Abnormal Psychology. Although this scheme 
is not the only one which may be used, it is the most convenient 
one for practical purposes. 

It is true that this scheme as given is not an accurate, logical 
one, as "animal", in. the wide sense, includes both the child and 
the adult human animal, as well as the so-called "lower animal". 
We actually use the terms to mean animal other than human. 
Social Psychology, again, is usually understood as Human Social 
Psychology; but it makes extensive use of the results of experi- 
ments and observations on animals. We might extend the scheme 
still further by dividing Animal Psychology into Normal and 
Pathological, but at the present time there is no practical advan- 
tage in such division; whereas there is an advantage in separating 
Abnormal Human Psychology from Normal Human Psychology. 
There is an advantage also in separating the psychological treat- 
ment of the pathological child — the child which either has insane 
tendencies, or is mentally deficient — from the treatment of the nor- 
mal child: but in the case of the lower animal it is not at present 
useful to study the psychology of the young animal apart from 
that of the adult. It is also true that there is in Human Psychol- 
ogy an intermediate field between the Psychology of the Child and 
the Psychology of the Adult, which is frequently given separate 

15 



16 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

treatment as the Psychology of Adolescence ; but this is rather an 
indeterminate field after all; and, therefore, is not given a special 
place in this particular scheme. This scheme, in other words, is 
one determined by convenience, and is not intended to be the ul- 
timate analysis of the whole field. 

Adult Human Psychology is the real basis for all the other 
divisions of Psychology. Child Psychology, for example : the study 
of the ' ' child mind ' ' : is to a large extent an interpretation of the 
activities of the child in terms of Adult Psychology ; and therein 
lie both the possibility and the danger of Child Psychology. 1 The 
study of animals from a psychological point of view is an interpre- 
tation of animal activity in terms of what we know about the 
adult human animal ; and in this case, as in the study of children, 
the very nature of the study introduces a serious danger, namely, 
the danger of hasty and uncritical interpretation. 

Social Psychology likewise can be developed only on the basis 
of a certain amount of knowledge of the psychology of the adult 
individual. In all three of these subjects, Animal Psychology, So- 
cial Psychology, and Child Psychology, the achievements of the 
present time are not very great. There has been a great deal of 
speculation in each of them: a great many theories presented in 

iThe possibility of Child Psychology (and of Animal Psychology) lies in the inter- 
preting of the behavior of the child (or animal) as conscious behavior, when the ob- 
servable part of the behavior is the same as that which is observed in the adult, and 
which is assumed to be conscious under similar circumstances. In such inferences, the 
postulates involved are the same as in the inference from my own conscious reactions 
to consciousness involved in the reactions of other adults. The danger in Child Psy- 
chology and in Animal Psychology, results from the great difference in behavior of 
children and animals, as compared with human adults, under the same circumstances, 
although certain outstanding details of the behavior may be the same in the two cases. 
The danger therefrom is in inferring that the child's (or the animal's) mental processes 
are the same as those of a human adult under similar circumstances, through failure to 
note that the child's (or animal's) reactions are not really the same as those of the 
human adult. The actual determination of the behavior of children and of animals is 
far more difficult than the determining of the behavior of adults. 

It has been assumed sometimes that the child mind may be examined without 
reference to the adult mind and therefore without the disadvantage of the source of 
errors in such comparison. This assumption is an unfortunate mistake which has 
merely served to cover up arbitrary assumptions as to the child's mind. One might, 
indeed, study child behavior exclusively: but when one discusses perception, thought, 
and emotional experience in children, one is making inferences from the adult mind; 
so that the only safety lies in being thoroughly cognizant of them as inferences. To 
deny, in such cases, that one is making inferences, is really to refuse to examine one's 
inferences: a procedure which leads to serious blunders in theory and in the interpreta- 
tion of experiments. 



INTRODUCTION" 17 

the guise of observation : but there is no extensive development of 
scientific results in any of those three fields such as we find in the 
basal field of Adult Human Psychology. In the field of Animal 
Psychology some important experimental work has been done, and 
a good foundation for future work has been laid. In Social Psy- 
chology and in Child Psychology there has been less achievement. 
That is as we should expect it to be. All three of the subjects 
wait on the development of Normal Human Adult Psychology, 
not keeping step with it, but lagging somewhat behind. What has 
been achieved in these lines, moreover, can be understood only 
through an understanding of what has been achieved in Adult 
Human Psychology. There is, therefore, a double reason for pay- 
ing strict attention at first to Adult Human Psychology. 

The relation of Normal Psychology to Pathological Psychology 
is similar to that of Human Psychology to Child Psychology and 
Animal Psychology. It has been said frequently during the past 
twenty years, that the study of Abnormal Psychology — the study 
of the insane and those on the borderland between definite insanity 
and sanity — and the study of functional disturbances of the mind, 
would throw light on Normal Psychology; and that the hope for 
advance in the latter lay in the study of the former. That hope, 
however, has not been fulfilled; but rather the development of 
Pathological Psychology has waited on the development of Normal 
Psychology. Very little has come back from the study of Abnor- 
mal Psychology to Normal Psychology, and a great deal of the 
theoretical construction in Abnormal Psychology is valuless be- 
cause it has not been founded on a scientific study of the normal 
mind. The study of the normal adult human individual is the es- 
sential point of beginning for all psychology, but we do not con- 
fine ourselves closely to that. In many cases the study of the 
child, the lower animal and the social group, in the light of what 
we know about the adult human mind, throws light back on the 
normal adult human mind, and we find ourselves drawing material 
from all these fields, for illustrative and clarifying purposes. 

There are many minor divisions of the psychological field 
which have no broad relations to those already described; divi- 
sions, moreover, which overlap considerably. We have, for ex- 
ample, Criminal Psychology, which includes the study of the actual 



18 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

criminal, and the study of the individual who is supposed to have 
criminal tendencies, although he has not developed into an actual 
criminal. We have also Educational Psychology, of which there 
are various kinds: this field is vague, including what we wish to 
put into it. In one sense the greater part of psychology is ' ' educa- 
tional ' ' in that it is constantly concerned with such changes in ani- 
mals as are produced by training or education. In a more limited 
sense, Educational Psychology has to do with the learning process, 
and the manifestation of instinct and emotion : processes which 
are of maximal importance in our school work. 

The Psychology of Art, or Esthetics, is another subdivision 
which has received a certain development, and is receiving more 
today. The Psychology of Religion is a well established branch 
of psychology, being the study of religion, not from the point of 
view of theology or ethics, but from that of the emotional and in- 
tellectual behaviour and experience of the persons who engage 
in religious activity. The Psychology of Sex which has recently 
become an important topic, is the study of the mental differences 
between the sexes, and the effects of these on practical life. In- 
creased knowledge of Sex Psychology is indispensable for the 
analysis and treatment of many social problems. Commercial and 
Industrial Psychology, a topic which is now being developed very 
rapidly, is the study of those mental processes which enter into, 
and are important in, commerce and industry. Because of the im- 
portance of the practical application of this branch of psychology, 
and its recognition before there was really much material avail- 
able for application, there has been much charlatanism in this 
field. 

Comparative Psychology, as the term is now used, deals with 
the relation between the four fields of Animal, Child, Abnormal 
and Normal Adult Human Psychology. In the past the term has 
been applied in a more limited way as a synonym for Animal Psy- 
chology. Genetic Psychology is the study of the development of 
mind, both the development of the individual human mind from 
the fertilized egg to the adult stage, and also the development of 
mind from the lowest stages of animal life up to the human mind. 

Educational Psychology, Commercial Psychology, Criminal 
Psychology and the practical aspects of Child Psychology and So- 



INTRODUCTION 19 

cial Psychology, are included under Applied Psychology. Applied 
Psychology is based on Individual Psychology, and involves as an 
essential part of its method Mental Measurements, which is the 
study of individual differences in mental life. A distinction is 
commonly drawn between Experimental Psychology and ;Mental 
Measurements, although the two are intimately related in method 
and technique. 

In mental measurements, the mental capacities and perform- 
ances of individuals are measured with a view to the comparison 
of individuals with one another, either for the purpose of selecting 
certain types of persons for certain purposes (as for admission 
to college, or employment as telephone operators), or else for the 
rating of these individuals for some other practical ends. Thus, 
the mentality of children and adults is measured by the Binet- 
Simon test to decide whether these individuals are normal, ab- 
normal or mentally defective, and Educational Measurements are 
applied in schools to determine the proficiency and progress of 
pupils in various curriculum subjects, in which specific tests and 
scales have been developed. Tests of moral attitudes and other 
characteristics are being developed. 

In Experimental Psychology, although measurements are al- 
ways made on individuals, the purpose is to discover and analyze 
traits common to all of the group investigated, the individual dif- 
ferences being difficulties to be overcome by experimental tech- 
nique, rather than being the main objective. Thus, in studying 
memory experimentally, the aim is in part to discover laws which 
determine the process of memorizing and of retention, with the 
conditions under which memory-work may be made most efficient ; 
rather than to discover the exact differences in memory capacity 
of the various individuals who are studied. 

§2. The nature of psychology. 

We have above spoken of Psychology as "the study of the 
mind." It was formerly denned as "the study of the soul." The 
word Psychology is derived from the Greek word psyche, which 
meant the vital principle or life essence. The most ancient treatise 
on psychology extant is Aristotle's Peri Psyche, which is best 
translated "concerning the vital principle." Because "psyche" 
has been sometimes translated as "soul", psychology came to be 



20 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

described as the study of the soul. But the word "soul" has ac- 
quired so many meanings that in psychology we no longer use it, 
although we do not necessarily deny the existence of any of the 
many things to which the term ' ' soul ' ' is applied. The term mind, 
also, which has been substituted for "soul" in psychology, has 
become so ambiguous that it is not easy to tell what any writer 
means by the term "mind" unless it is carefully denned. It is 
only when we specify precisely what we mean by mind that we can 
safely define Psychology as "the study of the mind." 

Mind is not something which can be sharply separated from 
body, and body is not something which can be sharply separated 
from mind, as we use these terms in psychology. In order to ex- 
plain the use of the term mind, we must consider the individual 
(whether man, child or animal) as a complex organism ivhich is 
stimulated by the environment, and which reacts to the environ- 
ment. 

When we say that an animal is a complex organism, we mean 
that it is made up of a vast number of individual cells. A human 
being does not ordinarily think of himself in that way, but as a 
matter of fact, the difference between a man and a swarm of bees 
is not so great as it appears at first suggestion. A swarm of bees 
is a group of separate individuals, anatomically distinct; yet these 
bees, in a swarm, with its various sub-groups and various duties, 
form a machine which functions as a whole in a way in which no 
single bee can function. The swarm lives, gives birth to new 
swarms, feeds itself and protects itself from its enemies. Not 
every bee does all these things, but they are done by the swarm as 
a whole. The queen lays eggs; but without care, protection and 
food supply from the workers, the eggs are of no value. So, too, 
the gathering of honey, and the other functions of the various 
workers, are of no effect without the functions of all. But with 
all its members functioning in proper interrelation, the swarm be- 
comes an entity in which the individual bees have their life, and 
which has its own longer life, in spite of the death of individuals. 
The animal body is an aggregate of individuals, most of which 
are as distinct from each other as are the bees in a swarm. The 
skin is made up of myriads of individual cells, which can be sepa- 
rated from each other, although the separation usually kills them. 



INTKODUCTION 21 

The muscles also are composed of myriads of distinct individual 
cells. The nervous system, including the brain, spinal cord and 
parts of the sense organs, is built up of vast numbers of individual 
cells. Most of these cells are fixed in position; they cannot change 
their location to any great extent. The muscle cells have power 
to change their shape, and because of this power of the muscle 
cells to change their shape, certain parts of the body may change 
their position, and the body as a whole can move about. There 
are, however, in the body, some cells which are free to travel about. 
Certain of these cells, (red blood corpuscles) which float in the 
blood stream, serve as carriers of oxygen. Other cells (white 
blood corpuscles) float in the blood stream and also have the power 
of locomotion, even the ability to leave the blood stream and wan- 
der into the other tissues. These cells serve as a police force for 
the rest of the body, attacking and devouring enemies, such as bac- 
teria. In the heart alone are found cells which are not distinct in- 
dividuals. The cells of heart muscle are so grown together (anas- 
tomosed) 2 that it is impossible to distinguish where one leaves off 
and another commences. 

The individual, then, is a complex organism, the parts of which 
work together harmoniously. If one part of such a body gets out 
of proper relation to the rest, the body breaks down and may die. 
The life of all the cells depends on the proper functioning of all 
of the classes of cells. The unity of the animal body is a unity 
of function: really a unity of the social functioning of the cells: 
and mind is one of the products of this social functioning. 

Leaving for the moment the conception of the individual as 
a complex organism, let us consider what we mean by stimulation. 
The animal is surrounded by a mass of details in the outside world 
which are constantly acting upon it. This mass is the environment 
In physical language, the environment is expending energy on the 
individual in numerous ways, and some of that energy produces 
modifications of the body which are called reactions or adjust- 
ments, involving usually contraction or relaxation of muscles or 
changes in secretion by gland cells. The process by which the en- 
vironment evokes reactions from the organism is known as stimu- 
lation, and the specific forces which act on the organism in this 



2 Such a group of anastomosed cells is called a syncytium. 



22 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

way are called stimuli. However, not every application of energy 
is stimulation. The x-ray is not a stimulus. If you put your hand 
under an x-ray bulb, there is no immediate reaction, although con- 
tinued subjection to the rays may kill the skin cells. If, however, 
you put your hand on a hot stove, the heat causes an adjustment 
of the organism : you feel the heat and it causes you to move your 
hand away. So, too, if light falls upon your eyes, or sound on 
your ear, the energy which is expended on your organism may 
produce reaction, and the reaction usually includes activity of 
parts of the body other than the parts stimulated. For example : 
when light rays fall upon your eyes, you may utter words or move 
your arms or legs, as a result of the stimulation. All those actions 
of the environment which produce reactions or adjustment of the 
body are summed up under that term stimulus; and the terms 
adjustment and reaction indicate the effects of stimuli. A stimu- 
lus is an external force which produces an adjustment of the or- 
ganism. 

Some of these reactions or adjustments involve the phenom- 
enon of consciousness. Consciousness is one of the terms which 
have many meanings, and which mean nothing unless carefully 
defined. 3 There are at present three principal ways in which the 
term consciousness is used. In psychology we are trying to use it 
in just one of these ways. 

Consciousness, as precisely used in psychology, means merely 
awareness of something, and wherever we find the word conscious- 
ness we can substitute perfectly the word awareness. For instance : 
when I look at the page in front of me, the situation is expressed 
in part by "I see the page," or " I am aware of the page," or, "I 
am conscious of the page." Consciousness is neither the "I" nor 
the "page." It is necessary to emphasize this, because much con- 
fusion has been bred on the point. There are three aspects of the 
situation involved: the 7, the page which I see, and the fact of 

3The confusion of terms in psychology is not all the fault of psychologists, and 
psychology was in existence long before there were any psychologists. Psychology in 
the past has been developed by men of most diverse types. Philosophers, physiologists, 
historians, physicists and others have contributed much. The points of view of these 
different types of men have been various, and they have used terms differently, intro- 
ducing terms from their own fields, and using the same terms with significations 
peculiar to these fields. The present state of confusion arose from such conditions, 
and psychologists are making serious attempts to introduce uniformity. 



INTRODUCTION" 



23 



seeing the page. These three are not identical, although the situ- 
ation is not complete unless all are present. Another illustra- 
tion may be drawn from the hearing of something, as when I hear 
the sound of the train. There is a sound heard, there is hearing' of 
a sound, and there is I who hear. The whole situation in the two 
cases is expressed by saying, "I am aware of the page," and "I 
am aware of the sound." Mental is the adjective corresponding 
to consciousness: anything directly connected with, or relating to, 
awareness, is mental. 

We can now define psychology in the terms which have been 
explained. Some of the adjustments of the organism are conscious : 
that is, they include or involve consciousness or awareness: they 
are mental reactions. Mind, then, is the totality of conscious ad- 
justments or conscious processes. The term is used in a concrete 
way to designate the totality of conscious processes of a single ani- 
mal, and also, in a more general way, to designate the conscious 
processes which occur in certain types of animals, or which occur 
under certain specific conditions. Thus, we speak of your mind, 
my mind, and a certain's dog's mind; and we also speak of the 
Child Mind, the Animal Mind, the Insane Mind, the Artistic Mind 
and the Mediaeval Mind. In a still more general way, we use the 
term mind without adjectives to designate the sum total of mental 
processes, whenever and wherever occurring. 

In applying the term mind to the life of a single individual, 
there are various degrees of extension. Genetically, a person's 
mind is the total of all the conscious reactions which have occurred 
since the beginning of his organic life. In a more restricted sense, 
the term may be applied to the group of processes occurring at a 
given moment. 4 

That which is properly included under the term psychology to- 
day is a very definite thing, and has a very definite foundation 
and course of development. It starts from the empirical situation 
we have described, in which there is conscious adjustment of an 
organism to the environment. This total situation, in which there 
is conscious adjustment, is best designated by the term experience. 
When we consider in detail such a situation, in which we have ex- 
perience, we find that there are four factors which are to be taken 



*The Mind at any given moment has been called a cross-section of the Mind. 



24 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

into account. 5 Three of these factors are immediately given as es- 
sential parts of the experience, and the fonrth is inferred or dis- 
covered as a condition of experience. These four factors are : 

1. Something of which we are conscious. That " something' ' is 
called content. 

2. Consciousness, or awareness of the content. 

3. I, or the ego, which is conscious, or has the consciousness. 

4. Bodily or organic activity. 

Physical science includes among its data only observable facts. 
Psychological science includes in addition two other facts, the 
second and third in our list above, neither of which are observable, 
but which are nevertheless empirical data, in that they are given 
in experience itself and are not inferences. The inclusion of these 
data is the only point in which psychology fundamentally differs 
from physical science, and if we ignore these data, we thereby 
abandon psychology completely, and go over to strictly physical 
science. 

1. The content of consciousness includes anything of which one 
is actually aware ; but in discussing the general features and laws 
of content, we must take into consideration everything of which 
it is possible to be aware. The analysis of content is important 



sThe relations of the conceptions embodied in the foregoing chapter to the concep- 
tions involved in other psychological discussions may be indicated by the following 
scheme : 

1. Soul: a substantial, unanalysable "ground" of consciousness. 

2. Ego: the unity of experience. 

3. Awareness: including perception and thought. 

4. Content: that of which one is aware. 

5. Physical objects: considered either as (a) combinations of contents, or, (b) 

as differing in Tcind from content. 

6. Matter: as properly conceived by physics: a mathematical statement of the 

relations of contents to each other, (including time, space, and causal 
relations) . 

7. Material substance: as conceived by some philosophers and naive thinkers: 

a ' ' stuff, ' ' made up of something which is neither sentiendum nor rela- 
tion. 
In this treatise we do not assume either (1) or (7). Science has nothing to do 
with either of these. We may consider (2) and (3) together as equivalent to "con- 
sciousness": (the knowing of -things together) : the ego being the "con-" and aware- 
ness the " -sciousness. " But since in normal experience the ego is always involved, 
we use the terms "awareness" and "consciousness" interchangeably. By physical 
objects, we mean (5, a), but some psychologists evidently mean (5,b), distinguishing 
"physical objects" from both " content" and from "matter," but holding that we 
can be directly aware of physical objects as well as of content: a point of view quite 
incomprehensible to the author. 



INTRODUCTION 25 

beyond the mere intrinsic interest in the results of such analysis, 
because it is possible to describe and discuss adequately the con- 
scious reactions of the organism only by relating these activities 
to the content which is perceived and thought about through such 
reactions. An essential part of psychology, therefore, consists in 
the analysis of content together with the reference of content to 
physical stimuli. 

2. Consciousness or awareness cannot be observed, since it is 
always and exclusively observation. One does not see the seeing 
of an object: one sees merely the colors and (in a somewhat loose 
significance of the word seeing) , the form, distance, and other fac- 
tors involved in the object. While it is obvious that in the act 
of seeing an object, that of which one is conscious is the object, 
the seeing being merely the particular way of being conscious of 
the object, it might be supposed — in fact, has been supposed by 
some philosophers — that in a later moment one might observe the 
seeing which occurred in the preceding moment. Such a turning 
of consciousness upon itself has, however, never been performed 
even in this retrospective way. If one sees a color or colored ob- 
ject, and then a moment later " thinks" of this experience, that of 
which he thinks will be either the color which was seen, or some 
other facts which were not seen but were heard, smelled, tasted 
or "felt" along with the original object. One is never conscious 
of the preceding consciousness itself. Consciousness, in other 
words, is not given in experience as an object, but as the conscious- 
ness or awareness of an object. 

While we cannot describe or define awareness, we describe and 
analyze the situations in which awareness occurs, and attempt to 
discover the laws of its occurrence and the consequences of its oc- 
currence. Such analysis is in fact the main business of psychol- 
ogy, to which the analysis of content is merely contributory. 

3. The "I" or ego, like awareness, is never an object or con- 
tent. It is never anything of which one can be aware, but is given 
in experience as that which is aware of something else. Further- 
more, the "I," as given, is nothing but that which is aware of 
something. Whatever else might be said in theory about the ego, 
is an inference (whether true or false), or a mere theoretical as- 
sumption. When we describe the ego as the soul, that is: as some- 



26 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

thing having self-existence, or substantiality, or immortality, or 
any other characteristic beyond the mere capacity to be conscious: 
we are ascribing to the ego something which is not given in ex- 
perience, and which, if it is to have any validity, requires demon- 
stration by rigorous scientific procedure. For the present, at least, 
psychology has no concern with the ego beyond its empirically 
given aspect. 

We may approach this point in another way by saying that 
there is in experience a peculiar reference or unity which is ex- 
pressed verbally by the use of the letter "I". Describing experi- 
ence in terms of consciousness and content does not quite sum up 
the complete facts. In addition to the facts which may be de- 
scribed by enumerating all of the details of content and all the 
awareness in a total experience, there remains over the fact that 
there is a unity, an identity, a common point of intersection. It 
is not true merely that there is seeing of color and hearing of 
sound and perception of tactual content at the present moment of 
my experience. Such enumeration would not differentiate be- 
tween the actual case, and the case in which one person sees color, 
another person hears a sound and a third person has another per- 
ception. The actual fact of identity in the total experience we are 
attempting to describe is expressed by saying that "I see," "I 
hear, ' ' " I perceive ' ? the other content : the term ' ' I ' ' in this state- 
ment marking or presenting the peculiar and essential identity 
which constitutes the organization of the experience as such. It is 
not far from the truth to say that in psychology we acknowledge 
the ego in order to ignore it in our further scientific work. Since 
it is not an object, and cannot be observed, there is nothing we can 
legitimately say about it, except, that it is that which is conscious, 
or, in more technical language ; it is the subject of awareness. 

4. In the experiencing of any content, bodily activity is always 
involved. This fact, however, is not given as a datum in the expe- 
rience itself, but it is a fact at which we arrive by processes of in- 
ference and hypotheses, confirmed by experimentation. Without 
bodily activity of some sort there is no consciousness, and hence no 
experience. 6 



eThis statement, of course, has no bearing on questions concerning what might hap- 
pen in seme other world than the one which we know. With the possibility or im- 



INTRODUCTION 27 

In saying that the bodily activity involved in experience is not 
content for that experience, we must not overlook the fact that 
bodily activity may in other cases be content. For example, a con- 
traction of a muscle in my arm is observable. It is a content for 
my experience. But in order that I may observe this muscular con- 
tent, another bodily activity must occur. This second bodily activ- 
ity may again result in muscular contraction, and this second mus- 
cular contraction may also be observed, but its observation re- 
quires in turn a third bodily activity. The bodily activity essential 
to any single experience or connected with any single act of aware- 
ness, is not itself observable in that experience or through that 
awareness, but requires a second act of awareness, and hence a 
second experience, in order that the ego may be aware of it. 

§3. Introspection and external observation. 

It has long been customary to distinguish between introspec- 
tion and external observation, but the actual distinctions to which 
this pair of terms has been applied have been various. The phi- 
losophers have constructed several different distinctions ; the phys- 
iologists others; and the resulting confusion in psychology has 
been detrimental to scientific work. 7 

The term introspection should be used exclusively to indicate 



possibility of discarnate minds, psychology has no business. In the actual circum- 
stances of living, the statement which we have made above holds true. What may 
be true in conditions other than life as we know it, is a matter of interest for reli- 
gion and philosophy, not for psychology. 

7Three of the principal theories of introspection may be mentioned. (1) That in- 
trospection is the study of the ego or I, as opposed to the study of other things. (2) 
That introspection is the study of awareness: the observing of observing, in a literal 
sense. (3) That introspection is the observation of sense data, as opposed to stimuli. 
To these may be added (4) the usage of the medieval philosophers who distinguished 
imagination and memory as internal observation, from sense perception as external 
observation. These four points of view are seldom found in modern psychological 
speculation in their pure form, but occur in various combinations with each other and 
with the simple view given in the text. In much of the Anglo -German psychology 
which has had sway until recently, it is impossible to distinguish these views clearly, 
an author seeming to imply now one,, now another. The systems of Stout and of 
William James are exceptional, in that these authors adhere each to a single theory, 
Stout to the second, James to the first, as they are enumerated above. 

The reasons for disregarding these theories of introspection are in brief (1 and 
2) that no one has as yet succeeded in demonstrating that either the ego or awareness 
can be observed; (3) that stimuli are by their nature unobservable ; and, (4) that 
although the distinction between imagination (and memory) and sense perception is a 
valid and necessary one, it is not useful to apply the term introspection in that con- 
nection. 



28 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

observation of one's own body, through the visceral and somatic 
senses. It does not indicate simply perception of the organism as 
distinguished from observation of other objects, since one can, for 
example, see the contraction of a muscle as well as "feel" the con- 
traction through the kinesthetic sense. In restricting the use of in- 
trospection in this way, we are but adopting explicitly a usage 
which has been common in experimental psychology, in spite of the 
varying theories which have been held. On account of the diffi- 
culty in making the term understood in the proper sense we shall 
avoid it in this text. 

§4. The methods of psychology. 

Although the name Psychology has been applied to a wide 
range of material, from philosophical speculation concerning the 
"soul" on the one hand, to the study of hypothetical "mental 
stuff" on the other, we shall here apply the name only to the 
scientific study of the mind as above described. 

Since psychology is a science, it must employ the fundamental 
methods of all science, although it also needs to employ certain 
supplementary methods peculiar to its own field, just as biology, 
physics and chemistry each need special methods and techniques. 
But in every case the special methods of a science must be in ac- 
cordance with and based on the general methods of all science, and 
cannot be in conflict therewith. It is useful to consider briefly the 
general principles of scientific procedure, in order that we may be 
able to maintain ourselves throughout on these as bases and to ex- 
clude those novelties and fads in the way of psychological theories 
which abandon or ignore these foundations. 

The general principles controlling the development of science 
are five : (1) It must be primarily empirical. (2) It must proceed 
from its empirical starting point by the construction of working 
hypotheses. (3) It must subject these hypotheses to experimental 
test. (4) It must furnish a specific type of proof for accepted hy- 
potheses, and, (5) It must be scrupulously exact in the use of 
terms. 

The empirical starting point of science is its basis in indis- 
putable facts which are data (that is, which are results of immedi- 
ate observations), and not inferences or results of inferences. For 



INTRODUCTION 29 

example: the observed fact that unsupported bodies do fall to- 
wards the surface of the earth is one of the data from which Ave 
proceed in the further acquisition of knowledge concerning the 
principles of gravitation and the laws of the pendulum. 

Experience, from which psychology starts, is the situation in 
which I am aware of something : a situation which includes three 
distinct factors: content (something observed); awareness (con- 
sciousness) ; and ego (I). 8 We have seen that physical science con- 
siders only the first of these factors; but all three are data, and 
psychology must recognize all of them. In other words, psychol- 
ogy starts from the total experience, and not from a limited part 
of it. 

The second point in scientific method is the construction of 
working hypotheses. Having observed phenomena, we seek to "ex- 
plain" them: and explanation consists in the framing of hypoth- 
eses in terms of which can be described not only the phenomena 
observed, but other phenomena as yet inadequately explained. In 
some cases the hypothesis which is formed is not strictly a new 
one, but is an extension of an old one to a new group of phenomena. 
The first type of construction is exemplified by Newton's concep- 
tion of the principle of gravitation, based on the observation of 
falling bodies : the second, by the hypothesis that the compensa- 
tory movements of the eyes (nystagmus) which follow the rota- 
tion of the head and body of an animal, are like many other reac- 
tion phenomena in that habituation to the stimulation will produce 
a lessening of the response. 

The most significant illustration of the importance of working 
hypotheses in psychology is the hypothesis that consciousness is 
essentially dependent upon reactions. This hypothesis has been 
formed through observation of the cases in which bodily move- 
ments occur concomitantly with consciousness, and an extension 
of the relationships observed in these cases as a generalization ap- 
plicable to all cases. This generalization, when made, becomes a 
starting point for further observations, and for experimental anal- 

«We have emphasized the fact that neither awareness nor the ego can be described 
or defined. But we shall find that this characteristic of indefinability is also shared by 
the ultimate or primary forms of content. In fact nothing which is really ultimate 
can ever be defined or described, but can merely be "pointed out," by describing 
complex situations in which it occurs. 



30 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

ysis ; and when verified and accepted, it leads to the modification 
of other working hypotheses. "When it becomes established as a 
fundamental principle, the whole further course of psychological 
inquiry is shaped and determined by it. 

The primary purpose in making such a generalization as that 
just described is to bring as many phenomena as possible under 
the same principle or formulation. Having found a certain prin- 
ciple applicable to a specific case, we seek to find out whether or 
not it can be extended to cover more cases. Science always seeks 
to explain as wide a range of phenomena as possible by the same 
principle. This procedure is in accordance with the law of parsi- 
mony, or law of economy in hypotheses, which may be stated 
briefly as follows : The simplicity of a hypothesis is an indication 
of its truth; and of two hypotheses, the one which explains the 
widest range of phenomena is the truer. That is to say: if hy- 
pothesis A covers all the phenomena explained by hypothesis B, 
and also covers additional phenomena, hypothesis A is preferable. 
Again, if a single hypothesis explains phenomena which without 
it would require the use of two or more hypotheses, the single hy- 
pothesis is the truer. Of two hypotheses covering the same ground, 
the simpler is the truer. "While it may seem strange that we should 
measure truth in such a way, it is a fact that in science we do so. 
The grand illustration of this fact is in the substitution of the 
Copernican theory for the Ptolemaic. If we should ignore the 
principle of economy, we should be forced to conclude that one 
theory is exactly as true as the other, since motion is purely rela- 
tive, and hence it would be as true that the whole solar and stellar 
system moves daily around the earth as that the earth rotates on 
its axis daily. But the application of the Ptolemaic theory, with 
its resulting theories of epicyclic paths of the planets, and still 
further intricacies, is so complicated and unwieldy as compared 
with the Copernican that the latter is adopted, not merely as more 
convenient, but as truer. 

The law of parsimony cannot be made the sole consideration 
in evaluating hypotheses, since a given simple hypothesis may 
sometimes be found to be incapable of experimental verification, 
while a more complex or less inclusive hypothesis may be verified. 
It is in the construction of hypotheses which are to be subjected to 



INTRODUCTION 61 

experimental test that the law of parsimony is the efficient guide, 
and its observance shortens the labor of finding the ultimately 
verifiable hypothesis. In psychology, this principle is of the ut- 
most importance, as we shall see in connection with later topics. 

Having constructed a plausible working hypothesis, this hy- 
pothesis is not forthwith accepted as a law, but is put to the test. 
Further observations, and experimental tests, are made on the 
phenomena, for the specific purpose of finding whether the hypoth- 
esis does actually fit these phenomena. 

The larger and more important hypotheses can seldom be put 
to experimental test as wholes, but deductions made from the hy- 
potheses — really minor hypotheses which are necessarily true if 
the major hypothesis is true — are tested experimentally. If these 
deductions are verified by the tests, then the minor hypothesis is 
so far substantiated and is retained for further testing. If the de- 
duction is proved false, then the hypothesis is false, and must be 
either reformulated or abandoned. Experiment is in every case 
the final test of a" hypothesis. 

Although working hypotheses may be subjected to test by mere 
observation, that is, the noticing of phenomena as they naturally 
occur, experimental tests are more vital for science, for several 
reasons. First, because in many cases the phenomena which it is 
necessary to observe do not occur unless the conditions for their 
occurrence are definitely arranged; or occur so seldom, or under 
such unfavorable conditions, that exact observation is impossible. 
It is possible to make a study of the effects of auditory stimula- 
tions on dreams, without experiment : but the arranging of condi- 
tions so that sleepers shall be stimulated by definite sound, or 
light, or other agency, at definite times, is a vastly more profitable 
method. Second, because observations are reliable only when the 
observer is prepared, at the moment of the occurrence of the total 
phenomenon, to observe this particular detail. Accurate observa- 
tion is always the answer, yes or no, to a question which the ob- 
server has previously formulated, and this is seldom possible ex- 
cept in experimental work. 

The value of a hypothesis depends largely on the possibility 
of its being tested experimentally. A hypothesis which offers 
many deductions which can be made the subjects of experimental 



32 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

work, is valuable, even if the tests ultimately lead to its rejection, 
whereas a hypothesis which may possibly be valid, is of no value 
until it is made amenable to experimentation. 

Scientific observation and experiment, if they support a hy- 
pothesis, do so through the accumulation of a type of proof which 
is very specific. The mere historical statement that such and such 
phenomena were observed, either with or without prearranged 
conditions, is not accepted as proof of any hypothesis. There must 
always be included the exact statement of the conditions under 
which another trained observer may observe the same phenomena. 
The hypothesis or deduction is not proved until these conditions 
are described so exactly that another person who follows these di- 
rections literally, and with no requirements laid upon him except 
that he shall follow the instructions as given, may obtain the re- 
sults which are claimed. The nature of this scientific requirement 
of proof is frequently overlooked, especially by those who argue 
from careless observations in support of the theories of subcon- 
scious mind, telepathy and other occult phenomena. 9 

"Anecdotal" evidence, the bane of pseudo-psychology, may es- 
tablish a presumption; that is, it may suggest a plausible hypothe- 
sis: but cannot serve as a means of proof of the hypothesis save in 
rare and exceptional cases. 

The necessity of rigid definition of terms is strikingly exem- 
plified in the history of psychology. In the physical science, care- 
ful use of terms has been the rule. Most mooted points in physics 
have been questions of fact only, since the same term means the 
same thing to both parties in the discussion. In psychology, how- 
ever, the most important terms have had an unfortunate fluidity of 
meaning, which has led to endless confusion and has facilitated 
the construction of bizarre and conflicting "psychologies". "Con- 
sciousness," for example, has had at least eleven different mean- 
ings in one period; and is widely used today in three radically 
distinct significations. "Sensation" likewise has three quite 
different meanings. These two terms are sometimes used by a 
single author in all of their meanings, the transition from one 



9The student may usefully compare the experimental evidence which has supported 
the hypothesis of radio-activity with the anecdotal evidence which pseudo-psychology 
offers in support of telepathy and premonitory dreams. 



INTRODUCTION 33 

meaning to another resulting in grave logical fallacies and appal- 
ling confusion. Sometimes two authors who seem to agree really 
mean qnite differently, and, conversely, many apparently vital 
differences of opinon are really due to a mere difference in use 
of terms. 

In this text, terms will be used strictly as they are denned or 
explained. Comparison with certain other texts is difficult, be- 
cause of the loose and vague use of terms in these texts. The stu- 
dent is especially warned that the carrying over of loose termi- 
nological usage from other texts and from popular discussion will 
prevent his making progress in the understanding of what is here 
presented. 

§5. Genetic and introspectionalist psychology. 

Strictly speaking, the genetic method is one of the several 
methods of procedure which scientific psychology may use legiti- 
mately, if sufficient care be exercised to prevent unwarranted con- 
clusions. The method covers both child psychology and animal 
psychology, as we have above described them. Introspection also, 
as the examination of the somatic and visceral sense data and 
feelings, is a procedure appropriate to scientific psychology, and 
indeed an essential part of its method. But the terms "Genetic" 
and "Introspectionalist" have come to be applied to two schools 
of psychology which have special points of view, over and above 
the favoring of the two procedures which give them names, and 
the essential characteristics of the schools are not to be found in 
their use of the genetic method and the introspective procedure 
respectively, but in the particular way in which they use these 
methods. 

Introspectionalists assume that the observable world is double 
in form: or, we may say, that there are two objective worlds. One 
of these is the physical world : the other a quite distinct psychical 
world. Between these two worlds there is supposed to be a cor- 
respondence such that for each object in the psychical world, there 
is an object, or complex of objects in the physical world. Both, 
however, are assumed to be directly observable and to resemble 
each other so much that it is quite possible, when attempting to 
observe psychical objects, to observe physical facts instead. This 
confusion is not only assumed to be possible, but to actually oc- 



34 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

cur, even in the observations of psychologists who do not work on 
the introspectionalist assumptions. This alleged confusion is 
called the "stimulus error": the stimulus, on this hypothesis, 
being the physical object which corresponds to the psychical ob- 
ject. 

For the introspectionalist, therefore, psychology consists in the 
observation of the psychical objects, just as physical science con- 
sists in the observation of the physical objects. As to the exact 
distinctions and relations between these two classes of objects, in- 
trospectionalists are not in complete agreement. In the examina- 
tion of the spectrum, for example, some introspectionalists say that 
the actual colors observed are the same, whether examined by the 
psychologist, for psychological purposes, or by the physicist for 
physical purposes, introspection and external observation being 
then identical for this case. Other introspectionalists, however, 
insist that even in this case the objects examined are different. 

The metaphysical conceptions of the introspectionalists need 
not concern us directly, for in many cases the actual results of their 
observations are precisely the same, when reduced to practical 
form, as the results of observations of psychologists who proceed 
empirically. The conceptions do, however, seem to have an influence 
on the introspectionalist 's further methods, which distinguishes 
these methods from those methods which we have above described 
as scientific. The introspectionalist, when observing, tends to at- 
tempt the observation of all possible content occurring during the 
period of observation, instead of limiting himself narrowly to defi- 
nite details which the observer may plan in advance to observe. 
Masses of reports on visceral and somatic data, thought-content, 
and content of external perception are thus obtained : information 
which is often picturesque, and which illustrates the complexity 
and massiveness of total content at any one time, and the great 
individual differences in attention and discrimination; but from 
which, in general, definite conclusions cannot be drawn. The 
study of such introspective reports strongly enforces our conclu- 
sion that empirical basis and scientific method are of the utmost 
importance for psychology. 10 



loFor the clearest statement of the introspectionalist assumptions, see Boring, The 
Stimulus Error, American Journal of Psychology, Vol. 32, 449-471. For characteristic 
introspective reports, sec Hoisington, Vol. 31, 114-146: Sulivan, Vol. 32, 54-80; 
O'Brien, Vol. 32, 249-283; and many other authors in the same journal. 



INTRODUCTION 35 

The genetic psychologists usually start from an introspection- 
alist basis, and attempt to trace the development of the world of 
mental objects, in some such way as the biologists trace the de- 
velopment of the particular class of physical objects called living 
organisms. Here, again, a general procedure into which many 
members of the school commonly fall, is not essential to the funda- 
mental method, but is nevertheless characteristic of the school. 
This procedure consists in the uncritical ascription to the 
young or lower animal of mental processes occurring in the 
adult human animal. The observer finds in the child certain 
actions which accompany certain mental processes in the adult, 
and naively concludes that the child has such and such proc- 
esses : without knowing whether the actions which he con- 
strues as signs are accidental or essential accompaniments or 
whether they may not be equally signs of two or more quite 
different processes. The genetic psychologist is such, in typi- 
cal cases, because he is impatient with the slow progress in 
the study of the adult human mind, and proposes to study, 
in some more direct way, the lower forms of mind, unhampered 
by critical evaluation of the relationships between conscious 
processes and external signs in the adult. In most cases, however, 
the genetic psychologist's impatience with adult human psychol- 
ogy arises from the fact that he envisages the latter in the intro- 
spectionalist form, not in the form which we have called scientific. 
In the latest, or "behavioristic" form, the tendencies of this school 
become most explicit. Reactions of infants are interpreted in 
terms of the conscious reactions of adults, but the discussion of 
the grounds for such interpretation is explicitly excluded. Certain 
genetic psychologists, for example, having observed in the young 
infant reactions which in the adult may be indicative of either fear 
or of pain experience, call the infant's reaction "fear," and make 
subsequent inferences as to the appearance and development of the 
"fear instinct", which would not be made if the observed reaction 
were described as "pain". 

Many psychologists, who are not to be classed with the genetic 
school, use the basal genetic method extensively, and with can- 



36 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

tion. 11 These psychologists are often loosely classed with the ge- 
netic school, but a clear distinction should be made here, just as is 
done in the case of psychologists who employ introspection (in 
the scientific sense) but are not introspectionalists. 



nFor illustration of the methods of the genetic school, we may refer to J. Mark Bald- 
win, Mental Development, and John B. Watson, Psychology. Judd, Psychology, em- 
phasizes the genetic method, but is not here classed as belonging to the genetic school. 



CHAPTER II 

SENSE PERCEPTION 

§1. Complex and elementary sense objects. 

Sense objects, or sense data, as perceived, are usually complex, 
that is: they are made up of two or more simpler sense data, com- 
bined in various ways. Sometimes these data are presented as oc- 
cupying different spatial positions, as is the case with the black 
and white of the printed page. These combinations are mere con- 
junctions. Sometimes, however, the several data combined in the 
total object occupy the same space, or are localized in the same 
position, as is the case with the purple of a purple aster, and the 
coldness, touch characteristics, and whiteness of snow. Such com- 
binations are commonly called fusions. It is useful sometimes to 
distinguish between fusions of data of the same mode, such as red 
and blue, and fusions of data of different modes, such as red and 
warm, cold and pressure. The latter combinations are convention- 
ally called complications. 12 

The analysis of conjunctions and complications offers no es- 
pecial difficulty in most cases. In the case of the snow, we readily 
observe that its total perceptible nature includes both whiteness 
and coldness, but that they are separable factors. Still more easily 
analyzable are combinations of color presented as adjacent to each 
other. In the case of fusions in the same mode, analysis is more 
difficult, requiring especially keen observation, and in some cases 
leading to results which have become matters of dispute. While 
all careful students agree to a separation of cold and warmth from 
the touch, tickle and pain factors with which they are fused, there 
has been controversy over the analysis of fused colors, as in the 
cases of purple (red and blue), and orange (red and yellow). 13 

The analysis of complex objects may be carried to such a point 

12 Warren calls them colligations. 

13 Orange is here described as a combination of red and yellow, in accordance with 
popular usage. Strictly, however, yellow is a combination of red and chlor (greenish 
yellow), and orange is a combination of the same pair, with a higher proportion of 
red. 

37 



38 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

that we obtain factors which resist any further analysis. Such 
factors, for example, are redness, sweetness, and the cutaneous 
pain which results from sticking a needle into the skin of the hand. 
None of these can be dissected by any means, or broken up into 
other factors. These ultimate results of analysis are called simple 
sense data. For conciseness sake, however, we shall refer to them 
as sentienda (singular, sentiendum). 14 

Sentienda are apparently fused in three different ways : First, 
into complexes in which each of the elementary sentienda are 
recognizable, as in purple, the sweet-sour of lemonade, and the 
cold-pressure of the handful of snow. Second, in complexes in 
which one or all of the component sentienda are unrecognizable 
for ordinary observation, although the complex itself is observ- 
able. For example, white, an observable datum, is a fusion of red, 
blue and a certain other color (sometimes called yellow and some- 
times called green, although as a matter of fact it is neither). Yet 
in the white, none of these sentienda can be directly observed. 
Again, we may add a little blue to a pure red and so change the 
total hue that the fusion is recognizably different from red, al- 
though the blue component cannot be distinguished. 15 Third, we 
may combine two odors, such as iodoform and balsam of Peru, in 
such a way that not only is neither odor observable, but not even 
the combination is perceptible. In such cases the result may be 
due to the actual destruction of one sentiendum by another. Two 
beams of light, for example, may be superposed in such a way that 
darkness is produced. It may be true, however, in certain other 
cases, that the product of the fusion of two sentienda actually 
exists although it cannot be perceived. This is a speculative point 
which has no present interest for us. 



i^Sentienda have been called "sensations," "simple sensations," and "pure sensa- 
tions, ' ' by the Anglo-German psychology. Sensation, however, has several other signif- 
ications in that psychology, and hence, to avoid the confusion which has become a 
serious matter, we shall not use the term at all. Sentienda might be called simple 
sense objects, were it not that the current confusions between consciousness and sense- 
data, and between sense data and physical stimuli make this usage incomprehensible 
to some readers. 

i^While this statement holds true for certain observers, it may be that everyone, with 
sufficient training, can learn to distinguish the relative blueness of the one color. In 
the case of white, the statement holds without qualification. 



SENSE PERCEPTION 39 

§2. The characters of sense data. 

All sentienda possess four intrinsic characters, namely: 
quality, intensity, extensity and duration (sometimes called pro- 
tensity). These characters are not components or elements in the 
sentiendum: the sentiendum can by no means be analyzed into 
them. They are merely aspects or points of view from which the 
sentiendum may be considered. Perhaps the best way in which to 
describe the characters is to say that they are ways in which senti- 
enda may differ from one another. For example : two spots of red 
may differ from each other in three ways: one may be a bigger 
spot than the other ; this is a difference in extensity. One spot may 
be brighter than the other; 16 a difference in intensity. One spot 
may last longer than the other ; a difference in duration. Yet the 
the two spots may be both the same as regards redness itself. 

Between a red spot and a blue spot these three differences (in 
intensity, extensity and duration) may obtain just as they do be- 
tween two spots of reel, and there is also the fourth difference, in 
quality, which is exactly illustrated by the difference between red 
and blue, regardless of the other characters. This qualitative dif- 
ference, in short, may be present although there may be no differ- 
ence whatever in intensity, extensity and duration. 

In addition to the intrinsic characters, there are two others, 
namely: position in time and position in space; which may for con- 
venience be designated as extrinsic. Sentienda (and also complex 
data) may differ in regard to the time at which they occur, and the 
place in which they exist. In the case of the fusion of two senti- 
enda, neither can differ from the other in temporal and spatial po- 
sition; but the two together differ alike in these respects from 
other sentienda. 

No sentiendum can be existent if it has not all six of these char- 
acters. In other words: a sentiendum which has no quality, or 
which has no intensity or no extensity or no duration, or which 
does not exist at some particular time, or which does not exist in 
some particular place, is a pure fiction. Two particular sentienda 
may, however, differ in only one of these characters. Two spots 



"Unfortunately the term "brightness" has been applied by some authors to what is 
more popularly called saturation, namely, the amount of white mixed with a pre- 
dominatingly single color. We shall, however, throughout use intensity in its original 
signification of color intensity. 



40 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

of red, for example, may be alike in quality, intensity, extensity, 
duration and temporal position, differing only in spatial position. 
Any two sentienda, however must always differ in at least one 
character: otherwise, there will be not two, but only one. 

§3. The senses. 

The total range of conscious responses to sense data is custom- 
arily divided into several groups called senses. Although the divi- 
sion is fundamentally a division of responses rather than of sense 
data, nevertheless the responses are grouped primarily with refer- 
ence to the qualitative differences in the sense data themselves, 
rather than with reference to the physiological mechanism. As 
might be expected, however, we find ultimately that the differ- 
ences in the sense data do correspond to differences in the details 
of reaction. 

The senses as thus distinguished have been known since Helm- 
holtz's time as modes of sense, or more conveniently as modal 
senses. This characterization is necessary in order to distinguish 
this division of sensitivity and of sense objects from another divi- 
sion which results in the groups known as the regional senses. 

Popularly, there are supposed to be five senses : sight, hearing, 
taste, smell and touch. Actually, the number is greater: a toler- 
ably complete list of the modal senses distinguished in accordance 
with the sense data includes at least fifteen. These modal senses 
are listed in the table on page 42, along with certain technical 
terms which are currently applied to sensory details. In the first 
column are given the common English names of the senses. In 
the second column, the more technical names derived from the 
Greek or Latin. Those terms in this and other columns which are 
legitimate, but not in wide usage, are enclosed in parentheses. In 
the third column are given the terms for the absence of sensitivity, 
that is: for the absence of response to the data of the given sense. 
The fourth column includes adjectives applying to the sensitivity 
and to the sense data. 

Concerning the senses of taste, smell, sight, hearing, touch, 
warmth, cold, pain and movement, there is no question. These 
are all separate senses, and are so recognized by psychologists and 
physiologists. The pressure sense, tickle sense and vibration sense 
are confused often with touch by those who have given little at- 



SENSE PERCEPTION 41 

tention to the data of these senses, and to the reactions involved 
in their functioning. The distinctness of these senses, however, is 
well substantiated. The fatigue sense has not been recognized 
generally, but extended observation of one's bodily sense data re- 
veals data of "weariness" which cannot be ascribed to any of 
the other modal senses in the list. The only senses listed which 
are really questionable are the sexual and vertigo senses. The 
first may be reducible to protopathic pressure and certain other 
subcutaneous senses as yet unanalyzed. In any case, it is re- 
stricted, topographically, to small areas of the sex organs, and is 
not to be confused with the sexual emotions resulting from stimu- 
lation of these areas. The data of the vertigo sense may turn out 
to be complexes of several visceral modes, but both of these senses 
must be listed provisionally. 

Complete analysis of the sensitivity of the visceral organs will 
undoubtedly reveal additional modal senses, which for the present 
must be slighted in our treatment. 

Some of the senses have sense objects of one quality only. 
Others, as for instance vision, have objects of different qualities. 
In speaking of the qualitative differences between objects of differ- 
ent senses (as, for example, the difference between red and sweet), 
the terms mode and modal are substituted for the terms quality 
and qualitative, the latter terms being specifically applied to dif- 
ferences within the senses : as, for example, the difference between 
red and blue, and the difference between sweet and sour. 

For purposes of convenience, the total range of sensory re- 
sponses is further classified by reference to the region of the body 
directly affected by the stimuli, without reference to modal dif- 
ferences. The groups thus obtained are designated as regional 
senses. The two principles of classification are sometimes con- 
fused. 

Reference to the dermal sense, hair sense (trichoesthesis), mus- 
cular sense (myoesthesis), joint sense, retinal sense (vision), coch- 
lear sense (audition), vascular sense, genital sense, gastric sense, 
and gullet sense, are to be understood in the regional way. A con- 
venient quasi-regional division of all the senses into four groups : 
cranial, somatic, visceral, and labyrinthine, is sometimes made. 
The cranial group includes vision, audition, olfaction and gusta- 



42 



ELEMENTS OF SCIENTIFIC PSYCHOLOGY 



tion only, the labyrinthine sense being excluded. The somatic 
senses include the dermal senses, kinesthesis, trichesthesis, and 
palmesthesis. The labyrinthine sense includes the sensory func- 
tion (if any) of the semicircular canals and vestibule of the ear 
only, although the cochlea is also a part of the " labyrinth." The 
sexual sense is included in the visceral group, rather than the 
somatic. 







TABLE OF 


THE MODAL SENSES 




I 




II 


III 


IV 


Taste 




Gustation 
(Geusis) 


Ageusia 


Gustatory 
Geusic 


Smell 




Olfaction 


Anosmia 


Olfactory 






(Osmesis) 


(Anosphresia) 


(Osmetic) 






Osphresis 




Osphretic 


Sight 




Vision 

(Opsis) 


Anopsia 


Visual 

Optic 

Optical 


Hearing 




Audition 

" (Acusis) 


Anacusia 


Auditory 
Acoustic 
Acoustical 


Touch 




Tact (ion) 


Anaphia 


Tactual 
Haptic 


Pressure 


Sense 


Baresthesis 


(Paranesthesia) 


Paresthetic 


Warmth 


Sense 


(Thalposis) 


(Athalposia) 


(Thalpotic) 


Cold Sense 


(Rhigosis) 


(Arrhigosia) 


(Rhigotic) 


Tickle Sense 


(Gargalesthesi? 


s) (Gargalanesthesia) 


(Gargalesthetic) 


Vibration Sense 


Palmesthesis 


Pallanesthesia 


Palmesthetic 


Pain Sense 


Algesis 


Analgesia 


Algetic 










Algesic 


Vertigo 


Sense 






Vertiginous 


Movement Sense 


Kinesthesis 


Akinesthesia 


Kinesthetic 


Sexual Sense 






Voluptual 


Fatigue 


Sense 









Another regional division of the senses classifies them as, ex- 
teroceptive, interoceptive and proprioceptive, and distinguishes 
the receptors of these as exteroceptors, interoceptors and proprio- 
ceptors respectively. The exteroceptive senses include the modal 
senses of vision, audition and olfaction, and the regional dermal 



SENSE PERCEPTION 43 

senses. The interoceptive senses include gustation and those divi- 
sions of the other senses (tactual, thermal, algetic and gargal es- 
thetic) which are regionally restricted to the inner surface of the 
alimentary canal (mouth, gullet, stomach, intestines and anus). 
All other sensory mechanisms, namely, those regionally distributed 
between the inner surface of the alimentary canal and the external 
surface of the body, are included under the heading of propriocep- 
tive. This classification, although doubtless very useful for physi- 
ology, does not lend itself to psychological use. 

§4. Sensory stimuli. 

In the scheme of the physical sciences, sensory objects or sense 
data, which constitute a fundamental part of the perceptible world, 
are represented by stimuli. If we should discuss adequately the 
relations of physical stimuli and sense data, we would necessarily 
enter one of the most abstruse fieldsof metaphysics. 17 For our pur- 
pose, we must consider only the empirical facts in connection with 
the complex problem. First : physical stimuli, as they are scientif- 
ically conceived, cannot be perceived through the senses. They 
are not sense data: they lack the fundamental character of qual- 
ity. A stimulus to the eye (ether vibrations), cannot be seen: a 
stimulus to the ear (periodic movements of air molecules), cannot 
be heard: and so through the whole series of stimuli. Secondly: 
so far as our knowledge goes, physical stimuli are mathematical 
expressions and nothing more. In other words, they are expres- 
sions, in terms of mathematical conventions, of the complex rela- 
tions and systems of relations subsisting between sense data. One 
might suppose^ of course, physical stimuli to be something more 
than this, although one would have difficulty in stating that suppo- 
sition intelligibly; but such suppositions can be neither proved nor 
disproved by scientific methods, and belong to the realms of phi- 
losophy and religion, lying quite outside the sphere of interest of 
science. 

The mathematical conception of physical stimuli is of great 
assistance, since we can thereby sum up in a few words or in pic- 

17 It is customary to rush into this metaphysical field (that of epistemolooy) by 
making* the assumption that physical stimuli are real, substantial, objects, and that the 
perceptible data are somehow derived from these. Following the empirical method, 
we must refrain from such speculative conclusions. Conclusions in this field can be 
reached only through a long and rigid course of epistemological research. 



44 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

torial expressions, a vast array of relations. We need nse the term 
physical stimnlus in this way only, although if any one chooses 
to believe that a physical stimulus is a divine force, a mystic 
energy, or something equally abstruse, he may prevent such be- 
lief from having a bearing on his psychological work. 

The term stimulus, however, does not, in current usage, always 
mean physical stimulus. In a looser, but customary, way of speak- 
ing, we apply the term to a simple or complex sense object of which 
the physical stimulus is the mathematical expression. Thus, we 
may speak of an orange as a stimulus to the sense of vision, mean- 
ing thereby the object perceived, and not the mathematically con- 
ceived ether-vibrations. In further discussions in which sense- 
data are referred to as "stimuli", the expression "mathematical 
expressions corresponding to" is to be understood as qualifying 
the references to sense data, if the term stimuli is taken in a strict 
sense. Stimuli of this type may be designated as unresolved: i. e., 
not reduced to physical stimuli. 

Stimuli are further divided into two general classes : adequate 
and inadequate. These terms are unfortunate,, but are in good 
usage. They should be understood to signify merely usual and 
unusual stimuli respectively. 

We can usefully list stimuli in three classes : of which the first 
includes stimuli which are both adequate and physical; the second 
includes adequate stimuli in the looser, unphysical sense, and the 
third, Class III, includes inadequate stimuli, both physical and 
unresolved. 

Class I. Physical Stimuli 

(1) Ether vibrations: periodic movements of the hypothetical 
ether, which is conceived as pervading space and objects in space. 
Light, physically considered, consists of ether vibrations of a de- 
terminate range of periods, which affect the receptors in the retina 
of the eye. Ether vibrations of certain other periods do not affect 
the visual receptors, but affect receptors in the skin and other tis- 
sues, giving rise to perception of warmth and cold. When for ex- 
ample, you hold your hand near a fire and perceive the warmth, 
the ether vibrations radiating from the flame reach the skin and 
produce their effects there. 



SENSE PERCEPTION 45 

(2) Molecular vibrations. When a piece of hot metal or a 
piece of ice is applied directly to the skin, it is possible that the 
molecular movements of the metal are communicated directly to 
the molecules in the skin, and that the molecular movements in 
the skin are communicated directly to the molecules of the ice. 

(3) Molar vibrations. In these cases, molecules making up a 
physical substance actually change their position in space peri- 
odically. This form of vibration, which is sometimes called molar 
vibration, therefore differs from the molecular vibration in which 
the molecules are supposed to vibrate without necessarily chang- 
ing their positions. Molar vibration of air is the usual stimulus for 
the auditory mechanism ; but molar vibration or oscillation of the 
molecules of the bones of the head, as in the case where the stem 
of a vibrating tuning fork is pressed against the head, may also 
serve as auditory stimuli. Molar vibrations transmitted to the 
skin and sub-cutaneous tissue, and to the bones, are stimuli of the 
vibration sense (palmesthesis). Such, for example, are the vibra- 
tions received when the hand is placed on the wood of a violin 
which is being played ; or when a vibrating tuning fork is touched 
by the hand. 

(4) Chemical stimuli. The activity of various chemical sub- 
stances stimulates certain sensory mechanisms in the organism. 
This action may be similar to that described under (1), (2), or 
(3) above; but for the present, it is best to allow for a separate 
group of chemical stimuli. The stimuli for the senses of taste and 
smell belong to this group. 

Class II. Stimuli As Yet Unresolved 

(1) Conditions of the tissues. Such conditions as of thirst, 
which is due to dryness of the soft palate and of the upper part 
of the gullet, and various perceptible conditions of the alimentary 
canal and other tissues, may possibly be referable eventually to 
the preceding class of chemical stimuli. Such reference at present 
would be premature. It is well to make a separate class of these 
unresolved stimuli. 

(2) Light moving contact. This type of stimulus is exem- 
plified in the brushing of the skin with cotton wool, which pro- 
duces tickle. It is characterized by the surprisingly slight amount 



46 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

of energy required to produce a powerful reaction, as compared 
with stimuli of the other dermal senses. 

(3) Movement of joint surfaces over each other. In the bending 
of the elbow, for instance, the movement of apposed joint surfaces 
stimulates the nerve endings and gives rise to the perception of 
movement. 

(4) Deformation of tissues. This form of stimulus may be il- 
lustrated by pressing on the skin, so that its level is altered, or by 
pulling on a hair with a corresponding result. In other cases, cer- 
tain portions of the skin or sub-cutaneous tissues have the pres- 
sure exerted upon them changed, or the actual form of the tissues 
modified by movement of the members which the skin covers. 
Striking or pressing on a tendon may produce stimulation of nerve 
cells ending in the tendon. 

(5) Muscular activity. In addition to the deformation of the 
skin and other tissues which lie above the muscles, the contraction 
or relaxation of muscle in some way stimulates receptors which 
terminate within the muscles themselves, giving rise, in some cases, 
to the perception of movement or of contraction. The exact physi- 
cal nature of the stimulation process is unknown, but the results 
are demonstrable. In the case of the visceral muscles, also, con- 
traction and relaxation are effective stimuli. 

(6) Acceleration of movement. When the movement of the 
body as a whole is accelerated or retarded, stimulations of various 
receptors in the body are produced. These stimulations are prob- 
ably all matters of pressure or deformation, due to the inertia of 
the body or of parts of the body. In the rotation of the body about 
any axis, similar stimuli occur; and in rotary movements of the 
head without the body, stimulation of the sensory mechanism in 
the semi-circular canals is produced. 

(7) Absence of customary stimulation. In some cases, cessation 
of action of a stimulus seems actually to stimulate the sensory 
mechanism. Thus the removal of light stimulus from the eye is 
supposed to be the cause of the perception of black, and the re- 
moval of sound stimulus from the ear the cause of the perception 
of silence ; and neither of these can be accounted for in direct terms 
of the positive stimuli of the visual and auditory mechanisms. 



SENSE PERCEPTION 47 

Class III. Inadequate Stimuli 

Inadequate stimuli can be conveniently classified under five 
headings. In this list, (1) and (3) are strictly physical. 

(1) Electricity. Almost any of the sensory mechanisms can be 
stimulated by application of electric current, and in some cases, 
by the application of a magnetic field. Electric current applied to 
the tongue will produce taste perception; applied to the eye, visual 
perception; applied to the skin, touch or other dermal perceptions. 
If the head be surrounded by a coil of wire through which alter- 
nating current of sufficient amperage and sufficiently slow fre- 
quency is passed, a brilliant flickering of light will be perceived. 

(2) Pressure. Some of the sensory mechanisms which are nor- 
mally not stimulated by pressure may nevertheless respond to this 
form of stimulation. Thus, pressing on the eye ball in certain 
ways will produce an experience of light. 

(3) Chemical. In certain cases, the application of chemical sub- 
stances will produce the effects of adequate stimuli of other kinds. 
Thus, peppermint or menthol may produce the experience of cold 
in the mouth; red pepper and alcohol the experience of heat. 

(4) Mechanical injury. Cutting or bruising of receptor cells, 
or of afferent nerve fibers, will produce pain. 

(5) Conditions of the tissue. Pathological conditions of the tis- 
sues may stimulate various sensory mechanisms in ways which 
are at present unknown. Thus, in inflammation of the skin, heat 
may be experienced. 

This is not a complete list of inadequate stimuli but merely 
an illustrative one, including the commonest stimuli which may be 
classed as abnormal or unusual. 

§5. The physiological sensory mechanism. 

Sense perception involves response or reaction of the mecha- 
nism to some stimulation. The ultimate or final part of a response 
consists in the activities of effectors — muscle cells and gland cells 
— or the inhibition of their activities. Muscle cells act by con- 
tracting and relaxing; gland cells by secreting, that is, by manu- 
facturing and delivering certain solutions, such as saliva and bile, 
which are of use to the organism, or urine, which is a waste 
product. 



48 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

The effector activities are set up by efferent current, which is 
discharged to these effectors from the brain stem or from the spinal 
cord through efferent nerves. In general, such efferent discharges 
result from preceding afferent nerve currents which are conducted 
into the spinal cord or brain stem over the afferent nerves, and 
which originate in receptors, these receptors having been stimu- 
lated either by external objects or by processes in the body itself. 
It is possible that certain efferent discharges occur as a result 
merely of chemical processes (such as stimulation by carbon diox- 
ide) in the cord and brain stem without the causal effect of pre- 
vious afferent currents. Such efferent discharges, if they do occur, 
are, however, modified and otherwise controlled by afferent cur- 
rent, and hence become components in the more general reaction 
processes. 

If we examine the details of reaction processes in the way in 
which they occur, we find: 

(1) stimulation of receptors. 

(2) conduction of nerve current into the cord and brain stem 
(afferent current). 

(3) central nervous processes, consisting mainly of transfer 
of current from point to point within the central division of the 
nervous system (including the spinal cord, brain stem, cerebral 
hemispheres and cerebellum. 

(4) conduction of current outward from the cord or brain stem 
(efferent current) to the muscles or glands or both. 

(5) contraction or relaxation of muscle cells, and secretion or 
inhibition of secretion of gland cells. This constitutes the "ac- 
tion ' ' phase of the reaction. 

A more extended treatment of the reaction process must be de- 
ferred to a later point; at present we are concerned merely with 
the initiation of the reaction process by stimulation of receptors. 

Receptors are cells:. all of them are of microscopic diameter, 
and some are entirely microscopic, while others are of considerable 
length. In order to produce sense perception, stimulation must 
always be applied to some portion of the body in which lie recep- 
tors capable of responding to that particular kind of stimulation, 
or in which such receptors have their external (peripheral) termi- 
nation. In all the senses except vision, audition and gustation, the 



SENSE PERCEPTION 49 

receptors are relatively long nerve cells, and have their external 
terminations in the tissues (skin, mucous membrane, muscles and 
tendons, subcutaneous tissues, and viscera) to which stimulation 
must be applied; and the other terminations are central (that is, 
in the spinal. cord or brain). The receptors of vision are micro- 
scopically short nerve cells, lying within the retina of the eye. The 
receptors for gustation and audition are epithelial cells lying 
wholly in the mucous membrane of the mouth and tongue and in 
the basilar membrane of the inner ear respectively. In these 
cases, the receptors are connected with the brain-stem through a 
nerve cell or series of nerve cells. 

Each sort of receptor is specialized to respond to a single type 
of stimulation, or to a single group of stimuli, and correspondingly, 
the reactions to which they give rise involve the perception of a 
single sentiendum or small group of sentienda. The receptors in 
the retina, for example, function for color only (including gray) ; 
the receptors of the cochlea for sound only. 



CHAPTER III 

THE CRANIAL SENSES 

§1. Gustation. 

Gustatory sense-data are usually called tastes. We speak of 
the "taste" of food or drink; of a "sweet taste", a "bitter taste", 
a "metallic taste", etc. The elementary tastes, simple gustatory 
data, or gustatory sentienda, are of four qualities only: sweet, salt, 
bitter and sour. All other tastes, that is, all tastes having qual- 
ities other than one of these, are fusions of two or more of these 
elementary tastes. Bitter sweets, sour salts and bitter sours are 
more familiar than salt sweets, salt sours and salt bitters, although 
all of these fusions are possible. Fusions of three of the simple 
tastes also occur; for example, the sweet-bitter-sour of ripe grape- 
fruit is well known. 

The gustatory data also fuse with tactual and dermal data and 
with olfactory data to produce flavors. In all the varieties of 
flavors of foods and drinks only the four taste qualities occur, the 
other components in the flavor — frequently the most important 
components — being odors, warmth, cold and touch. 

The qualitative relationships of the four gustatory sentienda 
to each other and also the possibilities of fusion are represented 
by the taste tetrahedron in Fig. I. 18 

In this figure, representing a solid or three dimensional scheme, 
each of the four elementary tastes is represented at one of the four 
vertices of the tetrahedron. The lines joining these points repre- 
sent the fusions of the simple tastes in pairs. For example, points 
along the line joining sweet (Sw) and bitter (B) represent fusions 
of these two in varying proportions, from the slightly sweetish bit- 
ter, through a balanced proportion, to a slightly bitterish sweet. 
Mixtures of three of the sentienda; for example, sweet, bitter and 
sour, would be represented by points in the surface determined by 

i8lntensity relationships are not included, as a four-dimensional scheme would be 
required for this purpose. 

50 



THE CRANIAL SENSES 51 

the position of these three simple qualities. Fusions of four can 
be represented by points lying within the solid figure. 19 

The receptors for taste are found on the upper surface of 
the tongue and the edges of the tongue, the surface of the soft 
palate, and even over certain parts of the lining of the pharynx 
and larynx. The central portion of the tongue surface is usually 
devoid of receptors. In young children and occasionally in adults, 
receptors occur also in the mucous lining of the cheeks, the sur- 
face of the gums, and even the lips. 

The stimulus for taste is chemical. Substances which are sapid, 
that is, which have taste, must be soluble in water. Substances 




Fig. 1. — Taste tetrahedron. The four points, B, So, Sw, and Sa represent the four 

elementary taste qualities ; and points on the lines joining these represent binary combinations 

of these qualities. Mixtures of three of the qualities are represented by points lying in the 

surfaces of the tetrahedron,' and combinations of four, by points lying within the tetrahedron. 

which are not soluble are incapable of exciting taste perception, al- 
though not all water soluble substances are sapid. 

In obtaining actual fusions of the four simple tastes by mix- 
ing substances which stimulate two or more of these, we must 
use substances which will not chemically combine in solution to 
form new substances, since such chemical combinations essentially 



19 Attempts at representations of qualitative taste-relations have been attempted by 
means of a plane figure. Such schemes are erroneous, since they necessarily represent 
the combination of one pair of tastes as equivalent to a combination of the other 
pair, which is not true. 



52 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

modify the stimuli. By mixing solutions of table salt, cane-sugar, 
hydrochloric acid and quinine chlorid, satisfactory results can be 
obtained. 

In making such mixtures, it is found sometimes that the inten- 
sity of a fused taste is less than the intensity of each of its com- 
ponents. This reduction in intensity is especially characteristic 
of fusions of sweet and salt. A very weak salt added to a very 
weak sweet may result in approximate tastelessness. A mixture 
of sweet and strong salt gives a definite alkaline taste, but this 
alkaline taste may be much less intense than the salt and sweet 
from which it is blended. In mixing sweet and sour, intensities 
are sometimes reduced, sometimes not. 

Adaptation effects are sometimes noticeable in gustation. A 
sour solution, such as one of lemon juice for example, often seems 
sourer after the mouth has been filled with something sweet. (This 
is described as contrast effect.) Continued stimulation with sweet, 
as in sipping a strong syrup, results in an apparent decrease in 
the sweetness of the solution, that is, in a decrease in sensitivity 
to the stimulation. 

These adaptation effects are exceedingly variable and the 
strength of the stimulus seems to be the most important factor. 
The phenomena are sometimes absent and sometimes reversed. 
Sometimes the stimulation of one quality will decrease sensitivity 
to one or more of the others. Where contrast is present, stimula- 
tion of one simple taste may heighten the sensitivity for sometimes 
one, sometimes another of the remaining three. Contrast effects 
are less apt to appear in respect to bitter than to any of the other 
three tastes. 

Certain substances affect the sensitivity of the taste receptors 
without themselves having distinct tastes. The leaves of gymnema 
sylvestris, when chewed, dull the sensitivity to sweet and bitter, 
dulling sweet especially, without affecting sensitivity to salt and 
sour. The leaves of the yerba santa of the Pacific Coast, on the 
other hand, increase the sensitivity to sweet. These effects are, of 
course, temporary. It has been alleged that tobacco smoking di- 
minishes the sensitivity to sweet through its effects on the tip of 
the tongue, in which location receptors for sweet are relatively 
most numerous. 



THE CRANIAL SENSES 53 

§2. Olfaction. 

Olfactory sense data are commonly and properly called odors. 
While it is possible that there are elementary odors (olfactory 
sentienda) comparable to the four simple tastes, none such have 
been discovered. Attempts have been made to classify the vast 
range of discriminable odors into a small number of groups, but 
such classification has little practical value. 20 

The receptors for odor lie in a restricted area (the olfactory 
membrane) in the upper part of the nasal cavities. The stimuli 
are chemical substances in a gaseous form, i. e., dissolved in air. 
Mere floating particles of matter, that is, dust particles, although 
they may be borne by the air into the nasal passages, are not odor- 
ous unless the particles give off gaseous emanations. In the act of 
smelling, we sometimes "sniff" by narrowing the anterior nares 
(external openings of the nostrils), and inspiring more forcibly 
than in ordinary breathing, so that the air-currents which carry 
stimuli are directed upwards into the region of the olfactory mem- 
brane, and thus we secure maximally favorable conditions of stim- 
ulation. Under conditions of ordinary respiration, the osphretic 
substances are diffused upwards from the air currents which pass 



soTlie classification most commonly referred to is that of "Linnaeus" (the name by 
which the Swedish botanist, Carl von Linne, 1707-1778, is commonly known), which 
is here given, with examples of the several classes : 

1. Aromatic — Turpentine; lavendar; camphor; spices; butyric ether. 

2. Fragrant — Flowers; vanilla; benzoin. 

3. Ambrosiac — Musk; ambergris. 

4. Alliaceous — Garlic; assafoetida; CI.; Br.; CS.2 

5. Hircine — Cheese; sweat; rancid oil; lactic acid. 

6. Repulsive or Virulent — Opium; nightshade family. 

7. Nauseous — Decaying animal matter. 

To this list the Dutch physiologist Zwaardemaker, in his book Die Pliysiologie des 
Gesuchs, in 1895, added two others: 

a. Ethereal — Fruits; some essential oils and ethers. 

b. Empyreumatie — Toast; tobacco smoke; tar; coffee; gasolene; creosote. 

A more recent (1916) form of the traditional list, constructed by a German 
physiologist, Henning, reduces it to six — flowery, fruity, putrid, spicy, burning and 
resinous. 

Classificatory work of this kind does not seem a promising method. Henning 
thinks the work of his predecessors was futile, and the next classifier will probably 
think the same of Henning 's labors. 

A more promising type of classificatory work was introduced by Sir William 
Ramsay, who found that there are resemblances of odors of organic substances be- 
longing to certain chemical groups. This work has been continued by Haycraft and 
others, but as yet no sweeping principles of classification have been discovered. We 
may reasonably expect, however, that sometime, definite relations between types of 
odors and types of chemical structures will be discovered. 



54 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

through the nasal cavities from the anterior nares to the posterior 
nares (the openings of the nasal cavities into the pharynx). Even 
when the breath is ' ' held, ' ' or when breathing is entirely through 
the mouth, stimuli may be diffused into the nasal cavities through 
the anterior and posterior nares, and produce their effects. 

The -flavors of foods and drinks are, as has been stated pre- 
viously, composed largely of odors. This may be demonstrated in 
a conclusive way by stopping both the anterior and posterior nares, 
whereupon all flavors are reduced to somewhat uninteresting com- 
binations of salt, sweet, bitter, sour, warmth, cold and tactual 
sense-data. Tea, coffee and quinine solution cannot be distin- 
guished from one another under these conditions, and the residual 
flavor of any fruit juice can be imitated by a proper mixture of 
water, sugar and acid (e. g., vinegar), with quinine added for such 
fruits as shaddock, and an astringent, such as alum, added for pine- 
apple. The various meats are indistinguishable; and vegetables 
can be discriminated from each other with great difficulty only by 
means of their tactual "feel" or coarseness and their resistance to 
mashing or chewing. If cooked and mashed to an equally pulpy 
condition, all vegetables taste alike when the olfactory stimulation 
is excluded. 

Stopping the anterior nares alone is sufficient to bring about 
the loss of odor with consequent impoverishment and confusion of 
flavors, if care is exercised in breathing, so that odors are diffused 
as little as possible into the nasal cavities through the posterior 
nares. Nasal "colds," involving swelling of the mucous mem- 
branes sufficient to obstruct the nasal passages, often produce these 
results in marked degree. 

Mixtures of odors produce results varying widely according to 
conditions. Sometimes there is obtained an apparent fusion in 
which the original odors can still be discriminated. Sometimes an 
entirely new odor is produced. In some cases, the intensity of the 
mixture of two odors is so low, as compared with intensities of the 
odors independently, that the two are said to be compensatory, or 
to cancel each other. In other cases, one odor will "drown out" 
another, so that the second is not distinguishable, but the first odor 
is perceived as if the second were not present. Various aromatic 



THE CRANIAL SENSES 55 

odors, such as the odors of burning substances, or of creosote, are 
frequently employed to mask or cover unpleasant smells. 

Adaptation is a striking feature of olfaction. Most osphretic 
substances, if present continuously for some time, become imper- 
ceptible. If the reactor is in a closed room in which there are fra- 
grant flowers, or a slight amount of illuminating gas, after a time 
he will not perceive the odor. Then if he goes out into pure air for 
some minutes, and subsequently returns to the room, he at once 
notices the odor. Similarly, on entering a crowded auditorium, the 
effluvia of the people present may be almost unendurable, at first, 
but later become unnoticeable. One unfortunate result of olfactory 
adaptation is that we may subject ourselves to noxious gases un- 
knowingly. Another result is that persons with strong body odors 
may not be aware of those characteristics, although other persons 
in their vicinity may perceive such odors distinctly. 

Adaptation is sometimes described as fatigue or exhaustion, but 
these terms do not seem to be accurately applied. The adaptation 
seems to be rather of a protective sort : the receptors in some way 
become shielded from the effects of the stimulus, and cease to re- 
spond : a condition which is more like the wetting of the powder in 
a fuse, rather than its being burned out completely, although in 
;either case the fuse refuses to burn. This conception, at any 
rate, is in harmony with the protective and immunizing processes 
which are found in connection with various organic functions. 

Adaptation to one odor may carry with it adaptation to certain 
other odors. It has been proposed to make use of this peculiarity 
of odors to discover the essential relationships of olfactory sense- 
data, and perhaps to arrive at the elementary odors. So far, how- 
ever, the total results of such investigations have not been of great 
importance. 

Anosmia or anosphresia: the permanent and complete absence of 
the sense of smell, has been found in many individuals. It is gen- 
erally accepted that there is a hereditary type of anosmia, and the 
occurrence of total anosmia in several successive generations of 
certain families bears out the supposition. In other instances, dis- 
ease of the nervous system has produced the defect. A congenitally 
anosmic person can never know what he misses in the world of 
odors and flavors. While his loss is not so practically important as 



56 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

is that of the totally blind man it is actually far greater in respect 
to the number of qualitatively different data which are impercep- 
tible to him. 

Partial anosmia, or parosphresia is of frequent occurrence. 
This may take the form of, (1) an entire lack of sensitivity for cer- 
tain odors, although other odors are normally perceived ; or it may 
take the form of, (2) a general weakening of sensitivity to prac- 
tically all odors. As compared with the keen sensitivity of certain 
individuals, a large percentage — probably the majority — of the hu- 
man race would be rated as partially anosmic. 

§3. Vision. 

The data of vision are properly called colors or hues, and gray. 
There are currently assumed to be elementary colors (visual sen- 
tienda), and all other colors are fusions of two of these in different 
proportions, and at different intensities. Gray is a fusion of all 
three visual sentienda in such proportion that no one of them is vis- 
ible as such in the complex. 21 

Two of the three visual sentienda are commonly called red and 
blue. The third is sometimes called "yellow" and sometimes 
"green," the variation in naming being due to the fact that it is 
really neither of the colors usually designated by these two names, 
but is, in common terminology, a greenish yellow. For this color, 
the term clilor 22 has been suggested, and will be used throughout 
our discussion. 

We must bear in mind that color names were fixed in European 
languages long before any analysis into elementary colors was 
made, and that the common names had their origin in practical 
considerations. Important natural objects such as the sky, grass, 
trees and gold were described, and simple names applied to their 
most typical colors. As pigments and -dyes were found or manu- 
factured, names were applied to their colors. Ochres, vermillion 
indigo, saffron, chalk and the Tyrian purple from cuttle-fish are 
types of pigments and dyes which were found early. Some peoples 



2iAlthough this is the current form of the color theory, it is possible that gray is a 
separate, elementary sentiendum. 

22The suggestion of "chlor" for this color was made by Dr. E. Q. Adams, of the 
Nela Eesearch Laboratory; but not with regard to the adoption of this color as 
elementary. 



THE CEANIAL SENSES 57 

applied the same name to quite different colors, because of their 
belonging to a common object. Thus, the Greeks of Homer's time 
had apparently but one word for green and blue, and that word 
was derived from one of their terms for the ocean. The Arabs also, 
according to Captain Burton, 23 apply certain names to more than 
one color, notwithstanding that they have, as a race, a keen color 
discrimination. We ourselves sometimes use the same words for 
discriminably different colors, although the range of inclusions un- 
der a single name is not so great as among more primitive peoples. 
Thus, we use "red" to indicate colors ranging from crimson to 
orange, and "blue" to indicate colors ranging between greenish 
blue and violet. 

The total number of distinguishable colors is large: probably 
more than a hundred. The common list of seven "fundamental 
colors" — red, orange, yellow, green, blue, indigo and violet — is 
due to Newton 's attempt to construct a color scale analogous to the 
seven-toned musical octave. If we include the various saturations 
of the colors, the number distinguishable is in the hundreds of 
thousands. 

For convenience, we will refer to elementary red by the letter 
R, to elementary blue by B, and to the third (greenish-yellow) 
elementary color chlor, by C. R will then mean, not all of the 
colors commonly included under ' i red, ' ' 24 but only the specific hue 
of red which is truly elementary ; and B and C will be used in sim- 



ssBurton, Arabian Nights, vol. VI., p. 111. ' ' The names of colors are as loosely used 
by the Arabs as by the Classics of Europe; for instance, a light grey is called a 'blue 
or a green horse.' Much nonsense has been written upon the colors in Homer by men 
who imagine that the semi-civilized determine tints as we do. They see them, but 
they do not name them, having no occasion for the words. As I have noticed, how- 
ever, the Arabs have a complete terminology for the varieties of horse-hues. In our 
day we have witnessed the birth of colors, named by the dozen, because required by 
women's dress." 

The attempts made by Gladstone and others to show from the Greek color-names 
that the Greeks were defective in color vision have been clearly shown by Burton's 
work to be fallacious. 

2 4 We must constantly bear in mind that the application of color names varies wide- 
ly even among people of "normal" color vision. Thus, what one person calls "blue", 
another will call ' ' green blue ' ', and what the second calls ' ' blue ' ', the first will call 
' 4 violet ' ', although both may actually see the same hues. Similarly, what one person 
calls "yellow" may be named "orange-yellow" by others. The sodium lines in the 
solar spectrum are described as "yellow" in some texts; as "orange" in others. 
In technical language, the name ' l purple ' ' is applied to the whole range of fusions 
of red and blue, including crimson and violet. In popular usage, the term is usually 
restricted to the middle portion of this range. 



58 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

ilarly specific meanings. To designate gray, we will nse N (neu- 
tral) ; for black, D (dark), and for white, W. 

The fusions of E with slight amounts of C produce the orange - 
reds and red-oranges. As the relative amount of C is increased, the 
fusions pass over to the true orange, and as the C component is 
still further increased, to the yellow-oranges and orange-yellows. 
When the C reaches a certain relative magnitude, the E being rel- 
atively small, we obtain yellow. 

By fusions of C with a relatively small amount of B, we obtain 
the yellow-greens. As the relative amount of B is increased, we ap- 
proach green, and by still further increases of B, the C becoming 
relatively small, we obtain the bluish greens and greenish blues. 

From E and B the whole series of purples are fused, from 
1 ' crimson, ' ' which is a slightly bluish red, to ' ' violet, ' ' which is a 
slightly reddish blue. In the "magentas" we have a more nearly 
equal proportion of E and B. 

The whole range of visible colors is represented in the planar 
scheme of Fig. 2, the three elementary colors being placed at the 
vertices of the triangle, and gray, (the balanced fusion of all three) 
at the center. Points along the line between E and C represent the 
fusions of these two sentienda only : points along the line from C to 
B and from B to E also representing binary fusions. Fusions of 
all three sentienda, in any proportions, including the balanced pro- 
portions required for N, can be represented by points within the 
triangle. Thus, the line from B to N represents fusions of B with 
schematically equal proportions of E and C, the proportion of B 
decreasing, and the proportion of E and C together increasing, as N 
is neared. In other words : the line represents the fusions in which 
the proportion of gray increases progressively and the proportion 
of B decreases, until finally pure gray is reached. The prolonga- 
tion of the line to OY (yellow-orange) represents still further de- 
crease in the proportion of B until it reaches zero, the proportion 
of E to C remaining the same throughout. 

The predominance of any one simple color, or any fusion of 
two together, in a fusion of all three, is called saturation. The 
more nearly equal the proportions of the three — that is to say, the 
greater the amount of gray in the color — the less or lower is the 
saturation. Any line from N to the boundary of the triangle, there- 



THE CRANIAL SENSES 



59 



fore, represents a series of saturations of a certain color, the high- 
est saturation of which is represented on the boundary line. 

The proportions of elementary colors required to produce a 
certain fusion or hue are not fixed, but depend on the condition of 
the receptors. A mixture of stimuli which produces a certain 
green with one condition of the receptors, may be in other condi- 
tions yellowish or blue. A mixture which is N at one time may be 
reddish, or greenish, or bluish, or of some other hue, at another. 
Moreover, under the same working conditions, different eyes may 




Fig. 2. — Color triangle. The three primary colors, Red, Blue, and Chlor, are represented 
at the vertices of the triangle. Other colors, being binary mixtures, are represented along the 
lines joining the vertices. Mixtures of all three colors, i. e., colors of reduced saturation are 
represented within the triangle, with the "balanced" mixture, or gray, at N. Colors lying on 
opposite sides of N, on a straight line passing through N, are complementaries. Since all 
colors seen under normal conditions are of reduced saturation, *. e., contain all three primaries, 
such colors lie within the triangle. All colors are here represented at the same brightness. 



see differently. A reddish gray for one person may be a neutral 
gray for another, and that which is green for one person may be 
even yellow for another. The conditions of variation in fusions 
will be described in later sections. 

It is seldom possible to obtain colors in full saturation, and 
actual colors must be assumed to be fusions of all three elements, 



60 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

although one, or perhaps in some cases two, may be relatively 
insignificant. 

From the consideration of the color triangle it is obvious that 
for each color, pure or mixed, there must be another color which, 
when mixed with the first in proper ratio of intensities, will pro- 
duce gray. For, since gray is a certain balanced ratio of the three 
simple colors, any mixture of two simple colors may have the third 
color, or a mixture of the third and one of the first two, so added 
as to produce the balanced mixture of the three. For example : a 
balanced mixture of R and C merely needs to have added the 
proper proportion of B: a mixture of R and C in which C is in 
excess needs not only B, but additional R, in order to produce gray. 
Two colors which will mix to form N are said to be comple- 
mentary. The color triangle is assumed to be so drawn that a line 
drawn through N from the point representing any color will, when 
extended, touch the periphery of the triangle again at the point 
representing the color complimentary to the first. Characteristic 
complementary pairs, with the approximate wave-lengths of their 
stimuli in millionths of a millimeter (/*/*) are 25 as follows: 

492 fi/i 
489 
485 
462 

The complementaries of the hues from OY to BG are not in the 
spectrum, but require mixtures of long and short waves for their 
stimuli. 

If we considered now not only the quality, but also the inten- 
sity, of colors, we shall need a tri-dimensional scheme for their 
representation. Such a scheme is presented in Fig. 3. In this 
figure, the line W-D represents the whole series of grays from 
black to white. This series, since the qualitative fusions are the 
same, is a series of intensities or brightnesses. Cross sections of 
the solid at any point parallel to the plane of the triangle R-C-B 
represent the whole color scheme, as in Fig. 2, but at different de- 
terminate brightnesses. The approach of all lines to two common 
points at D and W represents well enough the fact that above and 



Eed 


656 fifi 


blue-green 


Orange 


607 


greenish -blue 


Orange yellow 


585 


blue 


Yellow 


564 


violet blue 



25For explanation of the wave-length measurements, see pages 62 and 63. 



THE CKANIAL SENSES 



61 



below certain limits all colors tend to become less saturated, as 
they are increased or decreased in brightness, and finally become 
pure gray (white or black) in either case. 

Remembering that the fusions of colors are different at differ- 
ent times, according to the condition of the receptors, we will read- 
ily understand that even if the proportions of the solid were care- 
fully calculated, Fig. 3 would represent merely one condition: at 
best an average condition; and that the actual form of the solid 




Fig. 3. — Color hexahedron. All possible colors, in all possible saturations and brightnesses, 
are represented in this figure, in which the line from W to D represents the whole series of 
grays from white to black. 



scheme would vary greatly according to the receptor-conditions. 
The figure is to be understood as merely a scheme, not as repre- 
senting exact metrical relations. 

' ' White" and " black" are purely relative terms for varying 
high and low intensities of N respectively. 26 This can be strikingly 

26 B.lack and white are sometimes described as qualities, and gray as a mixture of 
the two. This usage has led to extreme confusion, and to still more bizzare hypoth- 
eses. If black and white are supposed to be qualities, it is necessary to assume 



62 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

shown by selecting small pieces of " black" and "white" card- 
board, and laying each on larger squares of properly chosen 
"black" and "white" cloth respectively. The cardboard will now 
no longer appear "black" and "white," but dark gray and light 
gray. These are not adaptation effects, such as are below de- 
scribed, but are instantaneous. If, now, a piece of the "black" 
cloth is placed on black velvet, and a piece of the white cloth is 
placed on white baryta paper, the cloths become gray. The black- 
est velvet, in turn, can be shown to be dark gray by comparing 
it with the greater blackness of an aperture in a box lined with 
black velvet. Adaptation effects may also change the degree of 
blackness or whiteness of any surface. 

The receptors for vision are nerve cells in the retina, or inner 
lining of the eye. There are two kinds of these receptors, rod 
cells and cone cells, the former sensitive to gray alone, the latter 
to gray and colors. The stimulus is ether vibration, which is prop- 
agated from a source of light, or reflected from an object, into the 
eye, and there works upon the receptors. It is presumed that the 
student is familiar with the physical theory of light, and the fol- 
lowing diagram and explanations are intended merely to refresh 
his memory. 

The vibrations of the ether are mathematically represented as 
at right angles to the line of propagation; a scheme which may 
be illustrated nicely by waves propagated along a loosely stretched 
rope. At any given moment the displacement is in opposite direc- 
tions at certain alternate points, and the wave length is the dis- 
tance between points of equal and similar displacement, as between 
e and e, and between d and d, in Fig. 4. Since, however, ether os- 
cillations of all wave lengths travel at the same speed in the same 
medium (e. g., glass, or air) ; the frequency of the oscillation at 
any fixed point through which the waves are traveling will be in- 
versely proportional to the wave length. It is possible, therefore, 



either: (1) that there are different intensities of each, just as there are of the colors, 
or else, (2) that there is no intensity of color, and that the varying "brightnesses" 
of colors are merely different saturations. This last supposition has virtually been 
made by some authors. The first supposition is obviously incompatible with the main 
hypothesis, since a lowered intensity of black would be exactly what is obtained by 
mixing a little white with black. No hypothesis will square with the facts except 
the hypothesis that the difference between white and black is a difference in inten- 
sity. 



THE CRANIAL SENSES 63 

to designate a system of waves either by its wave length or its 
frequency, but the ivave length designation is usually adopted for 
light, and the lengths are measured in millionths of a millimeter, 
for which the symbol w is adopted. 27 

Ether vibrations of wave lengths between 760 /*/* and 390 
fi,ti approximately, will stimulate the receptors of the normal eye, 
under usual conditions. The intensity of the light (amplitude of 
the ether waves) is, however, a part of the determining condition 
and as the intensity is reduced, the range of stimulation becomes 
somewhat shortened. Even with optimal intensities the range is 




Fig-. 4. — Wave motion in the ether. The loops e, e, e, d, d, d, represent the lateral displace- 
ments: The nodes n, n, n, n, n, are the points of no displacement. 

shorter for certain ' ' color blind " or " color weak ' ' individuals who 
will be described later. 

The Spectrum 

Daylight, and the light of the most common artificial sources, 
such as the gas flame and Mazda lamp, considered as a physical 
stimulus, contains ether vibrations of all wave lengths included 
in the visible range, as well as a considerable range of ' ' invisible ' ' 
(infra-red) rays longer than the longest visible rays, and a fur- 
ther range of "invisible" (ultra-violet) rays shorter than the 
shortest visible ones. 28 

It is possible, however, to separate the total beam of mixed 
light into its component stimuli of different wave lengths by one 

"Another unit of wave-length which is frequently employed is the " tenth-meter 7 ' 
Angstrom- Unit (Abbreviated A. U., or A.) which is one ten-millionth of a millimeter. 
1 m ix. therefore, is equal to 10A. Physicists incline to use the nomenclature (10~ 6 ) 
millimeters; which may be read "ten to the minus six millimeters" or "millionths 
of a millimeter. ' ' The wave length of the D line in the solar spectrum, for example, 
may be read: (approximately) 589 fi p., or 589 (10-6) mm., or 5890A. 

28 The expressions "visible rays" and "invisible rays" are convenient in speaking 
of visual stimuli, in spite of the fact that, strictly speaking, no ether-vibrations of 
whatever length are ever seen. 



64 



ELEMENTS OF SCIENTIFIC PSYCHOLOGY 



of several optical procedures. The most convenient of these pro- 
cedures is by the use of a prism, used either with or without lenses. 
In Fig. 5, I, is shown the simplest arrangement for producing 
a prismatic spectrum. Rays of light from a source, K, which 
should be as small as possible, approximating a point, are inter- 
cepted by the screen L, in which a slit, M, permits the passage of 
a narrow band of rays. These rays, approximately parallel, if K 
is some distance removed from L, are bent (refracted) out of their 
course by the glass prism, N, the red rays being least bent, the 
violet most bent. The fan-shaped beam is intercepted by the dif- 




Fig. 5. — Scheme of Spectrum production. 

I. Simple scheme. Light from the source K passes through the narrow slit M in the 
screen L,, is dispersed by the glass prism N, and forms the spectrum V-R on the screen P. 

II. Scheme actually used in spectral light apparatus. The lens B brings light from the 
source A to a focus in the slit D in the screen C. The beam of light, diverging from D, is 
rendered parallel by the lens E (collimator lens), dispersed by the prism F, and again focussed 
by the lens G as a series of images of the slit, forming the spectrum V-R on the screen H. By 
this method a spectrum of adequate brightness may be obtained. 

fusing screen, P, on which therefore the spectrum, with the colors 
in order R, 0, Y, C, G, B, V are seen. 

A spectrum produced in this manner is very faint and not ob- 
servable unless the eye is dark adapted. For practical purposes 
an arrangement such as that in Figure 5, II, is employed. An 
image of the source, A, is formed on the slit, D, of the screen C. 
The rays diverging from I) are rendered parallel by the lens E 
(collimating lens), refracted by the prism, F, and brought to foci 
by the lens, G, on the screen H. A spectrum of high brightness 



THE CRANIAL SENSES 



65 



may thus be obtained. This arrangement of lenses and prism is 
employed in the common sorts of spectroscopes, spectrometers and 
spectrophotometers, with an additional lens in an eye-piece (not 
shown in the cut) through which the spectrum at H is viewed. 29 

The light rays physically analyzed as described above, and fall- 
ing upon a " white" or gray surface, constitute the spectrum. The 
exact nature of the spectrum will depend upon the nature of the 
light-source used: for convenience, the spectrum obtained from 
sunlight — the solar spectrum — may be considered. 

In Fig. 6 is shown schematically the visible part of the pris- 
matic solar spectrum, with the approximate position of the Fraun- 
hofer Lines. These lines, which are due to light absorption in the 
earth's atmosphere and in the gaseous envelope of the sun, are 
convenient points of reference, since they correspond to definite 
bright lines in the spectra of various chemical elements, and have 



N O P 



o o 

Ch ON 
00 CO 



o 



« 



Fig. 6. — Diagram of a typical prismatic spectrum of sunlight. The part of the spectrum 
visible at moderate intensities is included under X: the part visible at higher intensities under V. 
The chief Fraunhofer lines are represented with the letters by which they are conventionally 
designated. The wave lengths of these lines are given in Angstrom units. 

definite wave lengths. The exact relative positions of these lines 
depend upon the material and angle of the prism. 

In the "visible" part of the solar spectrum, the wave lengths 
for the normal eye under normal conditions range from approxi- 
mately 760 /k/a in the extreme red to 890 /*/* in the violet: the part 
included under X in Fig. 6. The range for any normal individual 
may be slightly greater or less than this. In this part of the spec- 

29 As a matter of fact, a certain amount of white light is mingled with the spectral 
colors, on account of reflection internal to the prism, and further refraction is neces- 
sary to obtain a "pure" spectrum. But for many practical purposes, a spectrum ob- 
tained in the way described is satisfactory. 



66 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

trum, the colors seen are ranged in the order from red (760 to 690 
w*) through orange (660 to 590^), yellow (585 to 580^), green 
(525 to 500 «*), and blue ( 460 to 435 w) to violet (420 to 390 
/jl/jl). Under very favorable conditions of brightness and purity 
of the spectrum, and adaptation of the eye, the visible part of the 
spectrum may include also the part under Y in Figure 6, extend- 
ing as far as the R line, whose wave length is 318 w (3180 A ). 
Beyond this visible violet is the "ultra-violet" invisible part of 
spectrum: and beyond the red, at the other end, is the "infra- 
red" invisible part. We shall consider only the visible part of 
the spectrum from this point on. 

It is noticeable that the spectrum contains no purples, 30 except 
for the slightly reddish-blue which we call violet, but that aside 
from the purples it contains all known hues. From studies, into 
the details of which it is not necessary to go here, it is concluded 
that practically any wave length of the spectrum, from 760 w to 
390 fifji, corresponds to all three of the elementary colors, but to 
these colors fused in proportions varying widely, and in accord- 
ance with variations in wave length of the stimulus. In other 
words : in the colors seen at different parts of the spectrum, by 
the normal eye under the average conditions, all three elementary 
colors are present. Even in the "purest" red of the spectrum, as 
seen under ordinary conditions, there is a little B and a little C, 
combining with a balancing amount of the R to give, in effect, a 
slight amount of N which reduces the saturation of the red as 
seen. 

The proportions of R, C and B in the different colors of the 
solar spectrum as seen by the normal eye, may be roughly repre- 
sented by such a scheme as that given in Fig. 7. 31 The base line (ab- 

3oPerhaps a very slight violet or crimson-red at the end of the spectrum. 

siThe curves for the three fundamental colors presented in Figs. 7 and 8 are not in- 
tended to represent definite metrical relations between the intensities of the three proc- 
esses. Such relations would, of course, vary with the exact spectrum employed, de- 
pending upon the source and upon the prism (or diffraction grating) employed. More- 
over, the relation between intensities of the elementary colors, as directly compared 
and the " mixing values" of these colors, is a complicated and uncertain one. The 
proportions of the three which "balance", or produce white, for example, are not 
proportions which when compared photometrically, seem equally bright. The "bal- 
anced" ratio we have described as schematically equal values. Again, the schemati- 
cally equal values of B and C, which give in the mixture of the two a balance, or a 
predominance of neither, are not equal in brightness. Attempts have been made by 
Konig, Abney and others to work out metrical relations between the three colors, but 
it is doubtful whether measurements made by their methods have any significance aside 



THE CRANIAL SENSES 



67 



scissa) represents the spectrum extending from extreme red to ex- 
treme violet, and the ordinates of the three curves represent the 
relative proportions of each of the three elementary colors pres- 
ent at each point in the spectrum. At G, for example, C and B 
are present in schematically equal proportions, with a small 
amount of R. Looking at the scheme from the point of view of a 
single elementary color, as for example, C, we see that it is pres- 
ent in highest degree near the middle of the spectrum, being pro- 
gressively less represented towards both ends. In this diagram, 




Fig. 7. — Color sensitivity of the normal eye. The excitability of each of the three color- 
processes for wave lengths from the extreme red to the extreme violet is represented by the 
ordinates of the corresponding curve, points on the base line representing the various wave- 
lengths. R, Y, C, G, and B represent the points at which the purest red, yellow, chlor, green 
and blue occur. 

representation of exact metrical relation is not attempted, and in 
diverse conditions of the visual sense organs, the distributions are 
materiallv altered. 



The Physiological Hypothesis of Color Vision 

For further explanation of the phenomena of color vision it 
is convenient to depart from the discussion of the actual data of 
experience, and speak in terms of a physiological hypothesis, re- 
membering that this is merely a hypothesis, and hence nothing 
more than a linguistic device for grouping and studying the facts. 
Concerning the actual physiology of vision, very little is known. 32 

The perception of colors, according to a widely accepted theory, 

from the assumptions made by the investigators. In the curves of Figs. 7 and 8, the 
maximal excitations of the three processes in a given spectrum are arbitrarily rep- 
resented by equal ordinates. 

32 The so-called physiology of vision, as commonly presented is mostly psychology. 
The histology of the retina is well known, and so also is something of its chemistry. 
Eventually, perhaps, the real visual physiology will be worked out. 



68 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

is supposed to depend upon three sorts of activity 33 in the retinal 
receptors. One of these sorts of activity is assumed to be capable 
of initiating the reaction process through which K is perceived, 
and may here be called the r-process. The other two processes 
are capable of initiating the reactions through which C and B are 
respectively perceived, and hence may be called the c-process and 
the b-process respectively. When all three activities occur in " bal- 
anced" proportions, the reaction through which N is perceived 
may be initiated, and by other combinations of r, c and b are 
initiated reactions through which the various fused colors are per- 
ceived. 

Eeturning now to the spectrum, we find that the scheme of 
Figure 7 represents also the relations of stimuli and receptor- 
activities in accordance with our hypothesis. The abscissae repre- 
sent the wave lengths in the spectrum from 390 w* to 760 w and 
the ordinates of each curve represent the relative degree to which 
ether vibrations of each wave-length excite the r-, c- and b- proc- 
esses respectively. 

The Lag oe Latency of the Visual Stimuli 
We can measure the time relation of visual stimuli and per- 
ceptions with some accuracy — which is not possible for taste and 
smell — and we find that there is a decided lag or latent period be- 
tween the beginning of visual stimulation and the beginning of 
the perception ; and another definite period in most cases between 
the termination of stimulation and the termination of perception. 
The first period is the initial lag; the second is the terminal lag 
of vision. The initial lag is usually a matter of a few sigma, 
(o- : sigma is the symbol for .001 second), 34 but the terminal lag may 
be a matter of seconds, or even minutes. The light or color, in 
other words, is not perceived until a few sigma after the eye has 
been exposed to it, and it may be perceived long after exposure has 
ceased. 

That the terminal lag of vision is greater than the initial lag 



ssAs to the exact nature -of these hypothetical activities, no suppositions need be made. 
The supposition that there are three kinds of receptors is usually excluded, but the 
grounds for such exclusion are by no means final. We have employed the capital 
letters R, C, and B to designate the primary colors as seen, and the lower-case letters 
r, c, and b to designate the hypothetical physiological process. 

34Although the symbol a (sigma) is commonly used to indicate the thousandth part 
of a second, physicists are inclined to use the symbol (10-3) se c. 



THE CRANIAL SENSES 69 

is most strikingly demonstrated by the phenomenon of fusion of 
intermittent flashes of light. If a beam of light is interrupted by 
a sectored disc, rotating at increasing speed, the flashes of light 
resulting, soon merge into a picker, and then, when a certain rate 
of intermittence (the rate of which is called the critical frequency 
for light) is reached, the light appears perfectly continuous, and 
no further increases in rate of intermittence produce any effect. 35 
The critical frequency depends upon the intensity of the light, and 
on the condition of the eye: for bright light it may be as high as 
50 flashes per second. 

The terminal lag of vision is greatest for a bright light, to 
which the eye is exposed briefly. It may be demonstrated by 
means of a projection lamp and a screen of white cardboard, or 
white glass a few inches square. When the white screen is held 
a few inches from the objective lens of the projection lamp, a 
bright spot is formed by the concentrated rays : but if the card 
is moved rapidly (edgewise) through this point, the bright spot 
which flashes out momentarily on the card is seen "hanging in 
the air" after the card has passed through the beam. 

The after-effect of light of sufficient intensity and brevity may 
be prolonged beyond the period of terminal lag into the so-called 
positive after-image. This is best seen in a dark room after expos- 
ing the eyes to a bright light for one or two seconds. Then, if 
the eyes are kept open, and at rest, the light, with the same space- 
form it had during exposure, will reappear and persist for some 
time. 36 Eye movement causes the after-image to disappear, but 



ssThe phenomena of flicker and critical frequency may be most conveniently illus- 
trated by means of a solid disc with alternate black and white sections, illuminated 
from a steady source. 

36This after-image should properly be called the continuation image. It may be ob- 
tained from the filament of an incandescent light turned quickly on and off in a dark 
room, or from a window in an illuminated box covered with suitable white or colored 
glass with a diaphragm of such shape as to outline a figure. With longer original 
exposures, adaptation modifies or destroys the effect; adaptation and further stimula- 
tion may turn the positive image into a negative one. It is remarkable that the 
positive after-images, although more difficult to obtain than the negative ones, were 
described by Aristotle, while the negative ones were not mentioned. 

Intermediate between the primary light (as extended by the terminal lag) and 
the continuation image, there may be two or three brief positive after-images, separated 
by dark intervals. The first of these, following the primary light by approximately 
50 <r, has recently been called Henry's after-image, and the second, following a some- 
what longer dark interval, Purkinje's after-image. These are brief, and brighter 
than the continuation image above described, although dimmer than the primary light 
during its period of terminal lag. 



70 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

it may reappear if the eyes are held again at rest. This after- 
image may appear in the original color, or in one or a succession 
of the component colors of the original. 

Visual Adaptation 

Adaptation is of especial importance in vision, and here it can 
be shown very definitely that there is adaptation which is not 
fatigue. 

The general law of visual adaptation is that when the eye is 
subjected to feeble stimulation, its receptors tend to increase in 
sensitivity to that stimulus; and when subjected to intense stimu- 
lation, tend to become less sensitive to that stimulus. 

Adaptation to white or nearly white light is easily noticeable. 
On going from daylight into a dimly lighted room, the perceived 
light is dim at first, and in the course of some minutes, becomes 
brighter, and vision becomes clearer. Fifteen or twenty minutes 
are required for practical adaptation to a dim light, but the adap- 
tation actually improves for several hours. Conversely, on pass- 
ing from a dim to a bright light, the eye becomes adapted to the 
intense illumination, and the brightness of the perceived light is 
soon reduced, the adaptation in this case being much more rapid 
than in passing from a bright to a dim light. This adaptation 
phenomenon, in which there is no appreciable change of color, is 
called brightness adaptation. 

If the stimulation is not "balanced," that is, if the light is 
not "gray," the phenomenon takes still another form, described 
as color adaptation. Any color, pure or fused, tends to become 
less saturated, if it is steadily seen. Expressed in terms of our 
physiological hypothesis: if the receptors are stimulated in such 
a way that the three processes are unbalanced, and one or two 
predominate, continuation of the stimulus tends to bring the proc- 
esses towards balance, the more highly excited process or proc- 
esses becoming progressively less sensitive, and the more feebly 
excited processes or process becoming progressively more sensi- 
tive. 37 For example: if one stays in a room illuminated by light 
which at first, as one comes in from daylight illumination, is green- 



s^The phenomenon may be observed by wearing colored goggles which fit the face 
so closely that all light, except that coming through the lenses, is excluded. 



THE CRANfAL SENSES 



71 



ish, the light becomes progressively less saturated, and eventually, 
after an hour, more or less, according to conditions, becomes prac- 
tically gray. Obviously, in this case, the C and B processes have 
decreased in sensitivity, and the R process increased, until all 
three are finally excited in the normal "balanced" ratio. Color 
adaptation will occur whatever the absolute intensity of the light, 
but the total brightness may increase or decrease in accordance 
with the absolute intensity of the stimulus. That is to say: as 
the three processes approach the same level of excitability for 
the stimulus applied, the average level of excitability for all three 
may be raised or lowered. 38 

So far, we have considered adaptation only as affecting the 
whole retina. But the same phenomenon may be demonstrated 
where only small parts of the retina are involved, and the demon- 
strations are still more striking. 

If a small square of black paper is put on a large white or 
gray card, and one then gazes for some seconds fixedly at the 
center of the square, and then removes the black square without 
changing the gaze, or better, fixes the gaze on a definite part of 
another white or gray surface, then a white spot, i. e., a spot of 
brighter gray, will appear where the black was. This is the so- 
called negative after image, and is a pure adaptation phenomenon. 
The portion of the retina on which the image of the black square 
fell has increased in sensitivity as compared with the surround- 
ing area; and now when the whole area is subjected to equal 
stimulation, there is greater response in the darker adaptated 
area. 

The reverse effect — due to the same adaptation process — may 
be obtained by using a white square on a black background, and 
transferring the gaze to a light gray surface as before. If, instead 

^Brightness adaptation is, therefore, in part, due to the same causes as color adap- 
tation. So far as the fovea, in which there are only cone-receptors, is conjc&rned, 
brightness adaptation and color adaptation are probably the same essential phe- 
nomenon. But outside of the fovea, adaptation in the rod-receptors has apparently no- 
thing to do with color adaptation. The rod adaptation is in large part due to in- 
crease or decrease in a chemical known as visual purple, and brightness adaptation of 
both cones and rods is in part due to protective action of retinal pigment cells, which 
under strong illumination shield the receptors from the light. Such protective action 
of the pigment occurs at least in the eyes of some lower animals, although its occur- 
rence in the human eye has been doubted. 



72 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

of a black or white spot, a colored test object is used, a negative 
after-image of complementary color is obtained. 39 This is an adap- 
tation phenomenon precisely like that previously described, as af- 
fecting the total visual field. 

Simultaneous Contkast 

The adaptation of one area of the retina by stimuli applied 
to that area also produces similar adaptation changes in adjacent 
retinal areas. This phenomenon is readily demonstrable if a large 
area is adapted to color, while a smaller area completely enclosed 
within the first is stimulated by white light. If a small piece of 
gray paper, or still better, a narrow ring of gray, is placed on a 
background-sheet of colored paper, (red, for example), and a 
point in the gray paper (or a point in the center of the ring) is 
steadily fixated, the gray will soon take on a hue complementary 
to the color of the background. If, for example, the background 
is red, the gray will become tinged with bluish green. Obviously, 
the reduction in sensitivity to K and increased sensitivity to C 
and B has occurred on the gray-stimulated as well as on the red- 
stimulated area. This phenomenon is conventionally called simul- 
taneous contrast or negative col or -induction. 

Color contrast is at its highest when the background color and 
the gray are of approximately equal intensities. It may be still 
further heightened by one of several procedures: (1) by "squint- 
ing" with the eyes closed as closely as will permit vision; (2) by re- 
ducing the illumination falling upon the paper, as by lowering the 
window shades, or placing the test object in a shadow; (3) by plac- 
ing a sheet of ground glass, or a sheet of tissue paper covered by 
clear glass, over the test object; (4) by using for a test object a 
set of rotating discs ; e. g., a large colored disc with a smaller pair 
of black and white Maxwell's discs (see below) over that, and over 
the Maxwell's discs a still smaller disc of the same color as the 
largest disc; and rotating the whole combination at a rate greater 



saOften when looking at a spot of color on a gray background one sees the spot edged 
with the complementary color. This is the so-called edge-contrast. It will not oc- 
cur unless the gaze is unsteady, i. e., the eye wanders slightly. The student should 
be able to explain this as an adaptation phenomenon. 



THE CRANIAL SENSES 16 

that the critical frequency. The reasons for the intensification 
produced by these devices is at present entirely unknown. 40 

If a piece of paper of some color other than that of the hack- 
ground is used instead of the gray, the contrast effect is still pro- 
duced, the effect being that of adding the contrast color to the 
color of the small area. Thus, if blue is laid on red, the blue be- 
comes greenish (B + C) : if a complementary color is used, the 
color is intensified. Other mixed effects may be produced by plac- 
ing a small strip of gray (or color) between the wide surfaces of 
two different colors. 

The importance of contrast effects in contiguous color com- 
binations occurring in nature or in art can easily be comprehended. 
The more nearly complementary are two colors in a costume, for 
example, the more striking is the difference, and hence the more 
striking the effect. The nearer alike are two colors, the greater 
is .the "softening" effect upon each other. 

Color Mixing 

Various methods of mixing colors experimentally may be used, 
but one of the most convenient is by use of Maxwell's discs, custo- 
marily referred to as "maxwells." These are discs of colored 
paper or cardboard with holes punched in the center to fit an arbor 
on an electric motor shaft, and split radially from hole to per- 
iphery, so that two or more discs can be straddled together. These 
can then be placed so that any desired angular proportions of the 
several colors used may be exposed, and when the combination is 
rotated at a rate higher than the critical frequency, a smooth fusion 
is obtained. The retinal image of the disc-combination rotates 
at the same angular speed as that of the discs, and the receptors 
are therefore stimulated by the colors alternately. The effect pro- 
duced is equivalent to a mixture of the light reflected from the 
tAvo colored surfaces, not that of mixing the two pigments with 
which the surfaces are colored. 

By the use of five maxwells of the same diameter: Red, Green- 



4 °It has been said that the effect of the ground-glass or tissue paper is produced 
through the elimination or blurring of the contour lines between the gray and the 
color. This is disproved by the fact that accentuation of the contours by the draw- 
ing of fine black lines on the edges of the gray does not decrease the contrast effect. 



74 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

isli Yellow, Blue, Black and White, in various combinations, all 
colors, in all saturations up to the saturations of the discs em- 
ployed, together with the whole series of grays from black to 
white, can be obtained. From E and C, the series of colors from 
red through orange and yellow can be obtained by employing the 
various angular proportions of E and C. From C and B, the yel- 
low-greens, greens and blue-greens can be obtained; and from B 
and E, the purples, from violet through magenta to crimson. By 
combining the black and white discs with one or two of the colors, 
the colors may be reduced in saturation and in brightness, or may 
be reduced in saturation and increased in brightness. Many of 
the color relationships described in the preceding pages may be 
illustrated by means of these discs. 

Mixing of pigments does not produce the effects of mixing 
colored light. Thus: a mixture of complementary yellow and 
violet-blue paints produces, not gray, but green: this effect is simi- 
lar to that produced by passing white light through a yellow and 
a violet-blue glass in succession, and is a composite subtraction 
effect. It is important to remember that pigments produce their 
effects by absorbing or subtracting certain colors from the light 
falling upon them, and reflecting the remainder. 

Central and Peripheral Vision 

We have spoken so far of the adaptation effects which pro- 
duce manifold changes in the colors of objects seen, with the tacit 
assumption that the colors are presented to the fovea, or central 
area of the retina (the area of clearest vision). In the usual states 
of adaptation, however, colors are seen differently by the fovea, 
the paracentral area ( area surrounding the fovea) and the per- 
ipheral parts of the retina. 

The effect of moving a colored stimulus from the center to the 
periphery of the retina is strikingly like the effect of color-adap- 
tation. The color, after passing out of a small central area, be- 
gins to show decreased saturation, and may become pure gray as 
it nears the extreme periphery. As saturation decreases, on ac- 
count of displacement toward the periphery of the retina, the 
color may change: the hues from purplish red to green become 
yellow, and the hues from greenish blue to reddish purple become 



THE CRANIAL SENSES 75 

bluer. Yellow, blue, a certain green, and a certain purple show 
no change except reduction of saturation. The degree of satura- 
tion-reduction is dependent upon both the intensity and the dura- 
tion of the stimulus; high intensity and brief duration being pro- 
ductive of relatively higher saturation in the peripheral retina. 
The phenomenon may be described as due to a permanent partial 
color adaptation of the peripheral retinal receptors; or perhaps 
to a greater rapidity of adaptation changes in the periphery as 
compared with the center. 

The differences between central, para-central and peripheral 
vision are supposed to be due chiefly to the difference in sensitiv- 
ity between the rod cells and the cone cells. In the fovea, there 
are cone cells only. In the para-central region, rod cells are found 
also, and the rod cells increase in relative numbers with the dis- 
tance from the fovea, the extreme peripheral portion of the retina 
containing rod cells but no cone cells. 

Defects of Color Vision 

Certain individuals have characteristic permanent defects of 
central retinal vision which suggest both adaptation phenomena 
and the peculiarities of normal peripheral vision. These defects 
are included under the terms color blindness and color weakness. 

Some individuals, who are totally color blind, or achromopsic, 
see only gray. The solar spectrum and all other colored objects 
are for these persons merely different shades or intensities of gray. 
The difference between the visual world of these individuals and 
the world of persons with normal vision is comparable to the dif- 
ference between a black and white sketch and a color print. In 
the visual receptors of these persons, light of any wave length 
excites all three color processes in the balanced ratio. (Fig. 7.) 
In some cases, it is believed that cone cells are absent, only rod 
cells remaining. In other cases, the cone cells are apparently in 
a permanent state of equal sensitivity to all stimulation, as are 
the normal rod cells. 

Other individuals are par achromopsic, or partially color blind. 
The two most frequent classes of the partially color blind are pro- 
tanopes and deuteranopes , who together are classed as red-green 
blind. The characteristic symptoms of these defects are: (1) per- 



76 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

ception of low saturations of red and green as gray, and (2) con- 
fusion of certain dull reds and greens with browns. 41 

By careful work with the spectroscope it is found that both 
protanopes and deuteranopes are dichromats ; that is, they see in 
the solar spectrum only two colors, lying on each side of a neutral 
zone which occurs in the part of the spectrum which is bluish- 
green for the normal eye. The dichromat cannot distinguish the 
neutral band from normal daylight, if the intensities of each are 
made equal; and he cannot on the same side of the neutral zone 
distinguish any one part of the spectrum from any other part, if 
the intensities and saturations are equalized. It is believed that 
the two colors seen by dichromats are blue and yellow: that is, B 
and a fusion of E and C. In other words: any wave-length of 
light which excites the K-process, also excites the C-process in 
equal proportions, and vice-versa. 

The chief difference between the protanope and the deuter- 
anope is that the spectrum is slightly shortened at the red end 
for the former: that is, the extreme visible red for the normal per- 
son is not visible at all, even as yellow, for the protanope. The 
deuteranope, on the other hand, sees the spectrum as fully ex- 
tended at the "red" end as does the normal person (but of course 
sees it as yellow at that end). Certain slight differences in con- 
fusion of colors, as in sorting colored worsteds, are symptoms of 
the two cases. Protanopic color vision is represented by the curves 
in Fig. 8, which is to be compared with the curves for normal 
vision in Figure 7. The K and C curves, for the protanope, are 
superimposed, since any stimulus which excites one process ex- 
cites the other also to a schematically equal degree. The general 
positions of the curve are as if the E curve were moved to the 
right, nearly to the position occupied by the C curve in the dia- 
gram for normal vision. The shortening of the spectrum at the 
red end is thereby represented. 

The diagram for the deuteranope would be drawn in much the 
same way, except that the position of the combined E and C curves 
would be farther to the left, almost in the position of the E curve 
in the diagram for normal vision. This would represent, there- 



4i" Browns" are yellows and orange yellows of moderate saturation and low intensity. 
Orange of low intensity and moderately low saturation gives russet. 



THE CRANIAL SENSES 



I I 



fore, the unsliortened spectrum, with neutral band slightly to the 
left of the neutral band for the protanope. 

It is to be noted that these curves represent in a general way 
the actual conditions occurring in red-green color blindness, 
merely stated, for convenience, in terms of the three color hypothe- 
sis. In other words, the actual differences between the color vision 
of the normal eye and the color vision of the protanopic eye are 
represented by the difference between Figs. 7 and 8. 

It has been believed that red-green blindness may be produced 
by systemic poisons, such as tobacco and wood alcohol. This 
theory at present does not seem established. In many cases there 
is no known cause, but the condition is inherited, apparently fol- 

Inherited cases are sometimes de- 



owing the Mendelian laws. 




Fig. 8. — Color sensitivity of the dichromatic eye. The coincidence of the R and C curves 
represents the actual condition of sensitivity in both the protanopic and the deuteranopic eye. 
N represents the neutral band. 



scribed as "congenital," although it is not known whether they 
are actually congenital, or developed in the period of puberty, 
or just preceding that period. It is possible that many cases of 
so-called tobacco color blindness are not due to the use of tobacco, 
but are merely hereditary parachromopsia developing at a some- 
what late age. The occurrence of precisely similar cases in men 
and women who have never smoked is certainly significant. In 
these cases, the parachromopsia begins near the center of the 
fovea, and slowly spreads towards the peripheral retina. There 
is increasing evidence that all color blindness of the common red- 
green type begins in this way. So far as is known, nothing can 
be done to improve the vision of the color blind person. 

The practical importance of color blindness may be grasped 



78 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

by considering the great dependence placed upon color discrimi- 
nation by mineralogists, chemists and men engaged in transporta- 
tion by rail and water. It is singular that the colors most used 
as signals for danger and safety on land and sea (red and bluish 
green) are just the colors which offer the greatest difficulty in dis- 
crimination by the red-green blind. Many serious accidents on 
railroads have been due to color blindness of engineers, and al- 
though all train men now have their color vision tested, detection 
of color blindness is not easy, since many of the tests used are in- 
adequate. If orange and blue signal lights were used, the danger 
would be very much decreased. 

There are unquestionably types of partial color blindness other 
than protanopsia and deuteranopsia. In addition, there are mild 
degrees of the defect, known as color weakness. Some persons can 
distinguish the reds, greens, and spectrally intermediate colors 
at moderately high saturation and intensities, but not when the 
intensities and saturation are low. These individuals are unsafe 
as engineers and pilots, because smoke and fog often produce seri- 
ous reduction in intensity and saturation of signal lights. 

Another form of color weakness which is much more preva- 
lent than was formerly supposed is reduced sensitivity to blue. 
Many persons are unable to distinguish between a blue of low 
saturation and intensity, and a gray of equivalent brightness. 
These persons have escaped detection frequently because no color 
tests were adequate to detect them. 

It is sometimes said that there are relatively more men than 
women who are partially red-green blind. This may be true, but is 
doubtful. As tests of color vision are improved, more and more 
protanopic and deuteranopic women are discovered. Tests or- 
dinarily given are passed frequently by red-green blind women 
and men, who have had experience in the handling of colors. Cer- 
tainly, as regards reduced sensitivity to blue, there are as many 
defective women as men. In fact, there is ground for suspecting 
that there are more blue-weak women than men, rather than the 
reverse. 

As regards the average percentage of red-green blind to the 
total population, we may reasonably conjecture that there are 
about two per cent of such defectives. But the percentage varies 



THE CRANIAL SENSES 79 

so much in different stocks — being apparently less than one per 
cent among college men in some Western universities, and as much 
as four per cent in other groups — that no reliable statement can 
be made until more comprehensive and more adequate tests have 
been made. The principal basis for statistical statements at the 
present time is in the results of testing railroad men. Tests have 
not been made on a comparable group of women. 

Data in color defects obtained from officers and men of the 
United States Army in the recent war are unfortunately of no 
value for statistical purposes, as the tests used were inadequate 
and in many cases were not given expertly. 42 

It must not be assumed that absence of physical light-stimulus 
means absence of visible light. In complete darkness, some physio- 
logical stimulation of the visual receptors goes on and gives rise 
to what is known as idio-retinal light. This light is usually faint, 
and varies in different parts of the visual field. In some cases, it 
is quite bright in the dark adapted eye, and various colors may ap- 
pear as the r-, c-, or b- processes predominate or are minimized. 
The idio-retinal light is practically absent for a few moments 
after physical stimulation has ceased, and is inhibited in unstimu- 
lated areas surrounded by areas of considerable intensity of stimu- 
lation. In these cases the extreme degrees of " black" are per- 
ceptible. 

There are many interesting phenomena of vision into which 
the limitations of an elementary text forbid us to go. Some of 
these phenomena have been analyzed experimentally in great de- 
tail, and furnish an interesting field of work for the advanced 
student of sensory psychology. 

Note 

Theories of Color Vision. The form of presentation we have followed above is 
known as the ' ' three color ' ' or " Young-Helmholz ' ' theory. The original theory sug- 
gested by Thomas Young and developed by von Helmholtz differs in certain essentials 
from the modern theory. The modern three-color theory is the simplest yet constructed, 
and has the virtue of fitting all the facts. Many more complicated theories have been 
evolved, among them the theory of Hering, which has been much favored by physi- 
ologists. This theory assumes six fundamental colors — purple-red, golden-yellow, 
bluish-green, violet-blue, black and white; and assumes further that these are tied up 
in pairs with three reversible processes in the receptors: "red" and "green" with 



42 A number of typically red-green blind men passed the tests successfully and received 
commissions in the Air Service. 



80 ELEMENTS OE SCIENTIFIC PSYCHOLOGY 

one, yellow and blue with a second, and white and black with the third. The "red" 
process is based on the breaking down of a certain hypothetical chemical, and the 
"green" process on the building up of the same substance. Similarly, vision of yellow 
and white are assumed to depend on the breaking down of a second and third sub- 
stance respectively, and vision of blue and of black on the restoration of these sub- 
stances. In the condition of equilibrium of all three substances, no color is seen, but 
"gray" appears. The working out of the application to various color phenomena 
makes the theory very complex, and since it fails to fit all the facts of color-blindness, 
it need no longer be considered seriously. 

An interesting attempt to give the modern three-color theory a genetic basis has 
been made by Christine Ladd Franklin. She assumes that the totally color-blind eye 
is the most primitive type of eye : that the next stage of development produced the 
dichromopsic eye (with yellow and blue vision only), through the separation of the 
primitive ' ' color substance ' ' which is assumed to sensitize the receptors to light, into 
two substances, one sensitive principally to the long, the other to the short, waves of 
the spectrum. In the final stage of development, the ' ' yellow substance ' ' has separated 
into two: the "red-substance" and the "green-substance," thus producing the 
' ' normal ' ' color vision of the human animal. These two stages of evolution have oc- 
curred only in the cone-cells, however, the "color-substance" in the rod cells remain- 
ing in its primitive, undifferentiated condition, and hence color can not be perceived 
through rod-cell functioning. 

If the three-color theory needs essential modification, the assumption that white is 
the summation of R, C and B is to be called in question. The assumption of white 
as a fourth process may be necessary. 

§4. Audition. 

Auditory data are sounds, which include tones and noises. 
Under tones are included all sounds which have a distinct pitch: 
such sounds as the notes of a flute, organ, steam whistle, and 
human voice. Noises are sounds which have less definite pitch. 
There is, however, no dividing line between the two groups: there 
is a continuous gradation between the clear or "musical" tones, 
through noisy and noisier tones, over to noises which have little or 
no musical quality. 

Tones and noises alike are analyzable into simple tones. Al- 
most all musical tones contain a number of such simple tones, and 
the number of simple tones in a noise is very large. 

Simple tones differ from each other in pitch, in intensity or 
loudness, and in duration. Whether they differ in quality and in 
extensity remains to be examined. It is sometimes said that pitch 
differences are qualitative differences, that is: that pitch is the 
quality of auditory sentienda. But actually the pitch relation- 
ships of tones, which are as definitely known as are the qualita- 
tive relationships of tastes and of colors, are not comparable to 
those qualitative relationships. The series of pitches is continu- 
ous from the "lowest" to the "highest" and is adequately repre- 



THE CRANIAL SENSES 



81 



sented by a straight line. But this line does not represent an 
order of fusions of qualities represented by the ends of the line, 
as in the case with the line between sweet and sour, and the line 
between the colors R and C. There are no fixed points on the line 
at all: the musical scale may start with any pitch whatever in the 
total series and be equally accurate. The series of pitches, in short, 
is not a qualitative series at all, but is a quantitative series like 
a series of extensities, intensities, or durations. 

Since both the intensity and the duration of tones vary inde- 
pendently of pitch, we are forced to adopt the hypothesis that 
pitch is the extensity character of tones; and this theory fits the 
facts of tones and tone perception so far as we know them. 

The stimulus for audition is vibration transmitted through the 




c r c r c 



Fig. 9. — Wave form of pure tone. Drawn after Dayton C. Miller, The Science of Musical 
Sounds. The lower part of the figure represents the phases of compression (c) and of rarefaction 
(r) in the air, the arrows indicating the directions of movements of air-particles which have 
produced these phases. The upper part of the figure shows the way in which the sine curve 
represents these phases. The nodes (n) represent the points of maximal compression and rare- 
faction, and the ordinates of the curve represent the relative amplitude and direction of move- 
ment of the air particles. 



air, or other substances, and ultimately affecting receptors located 
in the cochlea of the inner ear. Sound-vibration differs from light- 
vibration essentially in that the particles of air or other substance 
oscillate in the line of transmission of the sound, and not trans- 
versely, as is the case with ether vibrations. Nevertheless, these 
vibrations may be represented by a periodic curve, just as light- 
waves are represented. 

The lower part of Fig. 9 represents directly the conditions 
occurring in a sound wave of a simple tone during one phase of 
the vibration. Air particles lying between n and n move towards 
c, causing compressions at c and rarefactions at r. In the next 



82 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

phase, not represented, the direction of movement is reversed, so 
that there will be rarefaction at each of the points marked c, and 
compression at each of the points marked r. For convenience, 
short lines are used to represent air particles. 

The sinusoidal curve in Fig. 9 represents the movements of the 
air particles, the elevations, and depressions of the curve repre- 
senting movements towards the right and left respectively. At 
the nodal points there is no movement. 

Pure, or simple tones have stimuli in which the oscillations of 
particles of the transmitting medium are pendular, and are repre- 
sented by simple sinusoidal curves. The period of the curve, that 
is, the distance from one phase to the next exactly similar phase, 
is the wave length; and the extreme distance by which the curve 
deviates from the axis is the amplitude. In any given medium, 
the amplitude corresponds to the intensity or loudness of the tone, 
and the wave length to the pitch. 

The stimulus for a complex tone is not simple pendular oscil- 
lations of the air, but a complex form of movement, which is the 
synthesis of all the simple wave forms of the stimuli of the simple 
tones which make up the complex tone. In Fig. 10 the curve at the 
top represents the actual wave form of the note of a certain organ 
pipe, and the curve numbered from 1 to 12 represents the wave 
form of the partials from the first to the twelfth, which make up 
that note. The algebraic addition of the ordinates of these twelve 
curves gives the upper curve almost exactly, the partials above 
the twelfth being negligible. Each of the simple wave forms into 
which a complex wave form is analyzable corresponds to a real 
partial in its complex note : but there are in many cases additional 
component tones (difference tones: see below) which have no cor- 
responding simple components in the stimulus. 

The vibrations of the sound stimulus travel through any uni- 
form medium (e. g., air or copper) at a uniform rate, regardless 
of the wave length, although the rates of travel in different media 
may be quite different. Ether vibrations also, of all wave lengths, 
have a constant speed of travel through a uniform medium. In 
any medium, therefore, the frequency of either stimulus is related 
in a simple numerical way to the wave length. The sound stimulus 
of 256 vibrations per second has, in any medium, a wave length 



THE CRANIAL SENSES SO 

of exactly twice that of the sound of 512 vibrations, in the same 
medium; and the frequency of ether vibrations of 300 w is twice 
that of vibrations of 600 w in any given medium. In either case, 
therefore, the standardized measurements of the stimuli might be 
made in terms of either wave length (in a specified medium) or 
of frequency. On account of various practical considerations of 
measurement, sound stimuli are customarily measured in fre- 




Fig. 10. — The wave form of an organ-pipe tone (reedless oboe, middle C, 260 v.s.), with 
its harmonic partials. By permission, from Dayton C. Miller, The Science of Musical Sounds. 
The upper_ curve represents the actual wave form, with a complete wave from a to b, as photo- 
graphed with Miller's phonodeik. The true axis is the dotted line a'b'. For any abscissa, as x, 
the algebraic sum of the ordinates, x-j, x 2 , x 3 , etc., of the partials, measured from' the true axis, 
a b , is equal to the ordinate, y, of the actual wave. It will be noticed that the maxima, Ai, A 2 , 
etc., of the partials do not come at the same point in the actual curve. 

quency, although light stimuli are measured in wave length in air. 
Light stimuli are measured sometimes, however, in terms of fre- 
quency. 

The normal ear can perceive tones whose stimulus frequency 
ranges from about 30 v. s. to 20,000 v. s. Children, and some 



84 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

adults, can hear tones of still higher frequency, up to 30,000 or 
more. Many persons, on the other hand, have a much shorter au- 
ditory range; some whose hearing is apparently normal in other 
respects are unable to hear tones above 15,000 vibrations per sec- 
ond. 43 

The principal component simple tones in a complex musical 
tone are called harmonic partials, 4 * and their frequencies have a 
simple and important relationship. If we take the frequency of 
the lowest pitched partial, or fundamental, which always deter- 
mines the pitch of the total tone, as 1, the frequency of the other 
partials, in order of rising pitch, are 2, 3, 4, and so on through 
the number series. If, for example, we consider the complex note 
of the open A-string of the violin, a tone whose pitch (the pitch 
of its lowest partial) is 435 vibrations per second, we will find the 
vibration of the several partials, from lowest up, to be as follows: 
435: 870 (-2x435): 1305 (—3x435): 1740 (=4x435) and so on. 

In some musical tones, and in noises generally, there are 
anharmonic partials, in addition to the harmonic series. Anhar- 
monic partials have vibration rates which do not stand in simple 
numerical relationship to a fundamental. In the tone of the or- 
dinary tuning fork, for example, there are practically no harmonic 
partials, but there may be an anharmonic partial, whose vibration 
rate is to the fundamental as 6% is to 1, and which may be made 
relatively loud if the fork is struck or bowed in certain ways. 

The apparent "qualitative" difference between different tones 
(properly called difference of timber**) is due to the number and 
relative intensities of the partials present. In the tones of musical 
instruments, the harmonic partials are most important. In the 
tone of one of the longer piano strings, a whole series of harmonic 
partials up to the eighteenth, or higher, is present, with different 
intensities. In the violin tone, fewer partials are present. The 



43 The limits of pitch perception are frequently put higher, but this is due to depend- 
ence upon measurements made by the Galton whistle — an unreliable instrument. 
44The partials, exclusive of the fundamental, are often called overtones, the second 
partial being the first overtone, the third partial the second overtone, and so on. This 
nomenclature is not so useful as the nomenclature in partials, since the ratios of the 
overtone numbers are not the ratios of their vibration frequencies. In any case, it 
must be remembered that the first partial and the fundamental are identical. 

45This word is often spelled timbre, and given the French pronunciation. English 
spelling and pronunciation are preferable. 



THE CRANIAL SENSES 85 

relative intensities of these partials in the series differs, however, 
for these two instrnments, and differs for the same string also, 
in accordance with the exact points at which the string is struck 
or bowed, and in the case of the violin string, the exact way in 
which it is fingered. The somiding-board also reinforces the par- 
tials in a selective way, so that the character of the tone depends in 
part npon the nature of the wood of which the violin or the sound- 
ing-board of the piano is made, and npon its form and method 
of support. 46 

The harmonic partials of strings, columns of air, and vibrating 
plates or membrane npon which musical instruments depend, are 
due to the fact that these sources of sound vibrate simultaneously, 
not only in wholes, but in halves, thirds, fourths and so on. The 
anharmonic partials likewise are due to the vibration of the sources 
in parts not in simple ratio to the whole. The harmonic partial 
vibrations may be readily demonstrated in the case of a stretched 
string, by setting it in vibration, and then touching it lightly, 
exactly at the center, with a camels hair brush, or a tuft of cotton 
wool. The fundamental (vibration of the string as a whole) may 
be thus checked, but the second partial, (vibration of the string 
in halves) and certain of the higher partials, continue to sound. 
The most apparent effect is that the note "jumps an octave", 
since the lowest tone in a complex note determines the pitch of 
the whole. 

By touching the string in a similar way at the point corre- 
sponding to any other integral (or harmonic) partial of the string, 
all the partials lower than the one corresponding to that segment 
(and some of the higher) are killed, and the partial corresponding 
to that segment becomes prominent. For example: if the string 
is touched at a point one-sixth of the distance from one end of 
the string to the other, all partials below the sixth are killed, and 
the sixth partial, being the lowest in pitch of those remaining, is 
clearly heard. 

After practice in identifying the partials in a string by the 
method described, many of them can be discerned in the total tone 
while the whole series is sounding. 



46 The different timber of the notes of two violins depends upon the different relative 
intensities of the partials in the notes. 



86 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

Since the timber of the tone of any instrument depends solely 
on the number of partials present, and the relative intensities of 
these partials, it is possible to produce the tone of any instrument 
synthetically, that is, by combining the proper 'pure tones' in 
proper relative intensity. The important partials are harmonic in 
these tones, and hence a set of tuning forks, with vibration rates 
in ratio of 1, 2, 3, 4, etc., may be used for this purpose. In such 
cases, the forks should be driven electrically, in order to maintain 
uniform and controllable amplitude of vibration, and resonators 
are desirable to intensify the sounds. With such a set, the tones 
of the violin, flute, clarinet and other instruments, and of the 
human voice, may be closely imitated. In the telharmonium, a simi- 
lar result was obtained by superposing the currents from a number 
of alternating current generators, with the proper frequency rela- 
tion and sinusoidal form of alternation, in the same telephone re- 
ceiver. 

The partials in any complex note must be regarded as different 
extents, coincident at one end, as will be explained more fully be- 
low. If each partial be represented by a parallelogram, the length 
being the pitchy and the breadth the loudness, a complex note may 
be represented by such a figure as Fig. 11. The diagram repre- 
sents also the actual scheme of stimulation of the receptors in the 
auditory organ. 

The musical scale is based on the octave: the relation between 
the first and second partials, which have the vibration ratio of 1 :2. 
Various divisions of the octave, made by inserting notes between 
these two, have been used in the music of different races, and are 
called scales. The scales used in modern western music are de- 
rived from the diatonic scale, in which six notes are inserted with- 
in the octave, the ratio of the notes having the relatively simple 

cde f g a be 
values of the numbers: 8: 9: 10: 10-2/3: 12: 13-1/3: 15: 16. From 
the diatonic scale, the true chromatic scale is derived by inserting 
additional notes between the first and second, second and third, 
fourth and fifth, fifth and sixth, and sixth and seventh notes in the 
diatonic scale. In each of these positions two notes are inserted, 
one, the sharp, having the vibration rate of 16 :15 to the diatonic 



THE CRANIAL SENSES 87 

note immediately below it, the other, the flat, having the rate of 
15 :16 to the diatonic note immediately above it. 47 

In the true chromatic scale, the flat of one diatonic note is al- 
ways lower in pitch than the sharp of the diatonic note below it: 
thus, ab is lower than g$. The ratio of db to ct|, of gb to fk|, bb to at] 
is 25:24; and this ratio is adopted for the sharps, and 24:25 for 
the flats, in a secondary chromatic scale, which is more widely 
used than the true chromatic. In this scale, therefore, some of the 
sharps and flats in the true chromatic scale are used, but the names 
are interchanged; bb being the aft of the true chromatic scale, and 
vice versa. The sharps and flats between d and e, and between 
g and a, are slightly altered; and additional sharps and flats are 
inserted between g and a, e and f, and between b and c, where 
none are possible in the true chromatic scale. 

The diatonic and chromatic scales are suitable for the human 
voice and certain types of instruments, such as the violin and the 
trombone; but if the piano and the various string and wind in- 
struments, having fixed keys or frets, were tuned in this scale, 
transposition to higher and lower keys would be impossible. More- 
over, the distinction between sharps and flats makes the execu- 
tion of music in the chromatic scales very difficult. Hence, a sim- 
pler scale, the equally tempered scale, is derived from the chro- 



47The ratio 15 to 16 is the ratio of b to c, and also of e to f (10:10 2/3). 

These ratios hold for any octave of the diatonic scale, regardless of the absolute 
vibration frequencies. In other words, if a certain frequency is adopted for any note 
in the scale, the frequencies of all the other notes are determined through the fixed 
ratio. 

For scientific purposes, a standard scale based on a middle c (c') of 256 v. s., is 
generally used. In musical practice, various standards of pitch are employed. "Low 
pitch" or "International pitch' ' is based on a' (the note of the open A-string of the 
violin) of 435 v.s. This is also known as "Koenig's Normal Pitch". "High" or 
"Concert pitch" is somewhat above this, one standard of "Concert pitch" being 
based on a' of 461 2/3 v. s. In the times of Handel and Mozart, the pitch standard 
was lower, a' then being 442 v.s. 

The scales based on these most important pitch standards for the octave ascend- 
ing from middle c are: 







c' 


d' 


e' 


f 


g' 


a' 


b' 


c" 


Scientific 


Pitch 


256 


288 


320 


341 


384 


426 


480 


512 


Internatiom 


a " 


261 


293 


326 


348 


391 


435 


489 


522 


Concert 


tt 


277 


311 


346 


368 


415 


461 


519 


554 



The notes in the next octave above will have double the v. s. given for the octave 
e'-c": in the second octave above, four times: in the third octave, eight times, and so 
on. Pianos are supposed to be tuned in a tempered scale corresponding in pitch to 
the International pitch of the diatonic. 



88 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

matic scale, and is the scale principally nsed for all music except 
that of the voice and of instruments of the violin and trombone 
families, when unaccompanied by other instruments. 

In the equally tempered scale, the sharps and flats are identi- 
fied : for example, a{ and bb are in the same note : and the twelve 
intervals between the successive notes in the octave are equalized, 
so that each note has exactly the same ratio to the note of a "semi- 
tone" above it. In this scale, all instruments with keys or frets 
are supposed to be tuned, although the accurate tuning of pianos 
is practically impossible. 48 

A still further modification of the scale has resulted in the tonal 
scale used by Debussy and the "French School" of music. In this 
scale, only the alternate notes of the scale of equal temperament 
are used, the octave thus consisting of c, d, e, f#, g#, a}, c. Char- 
racteristic effects, concerning the values of which the opinions of 
musicians differ, are obtained by the use of this latest scale. 

Beats axd Difference Tones 

When two tones, sounded simultaneously, differ by only a slight 
amount in vibration rate, beats result. Beats are alternate in- 
creases and decreases in intensity of the primary tones, and are 
due to the alternate reinforcement and interference of the two 
sets of sound waves, their amplitudes being alternately added and 
subtracted. The frequency of the primary beats is equal to the 
difference between the vibration rate of the two tones. Thus, if 
a note of 256 and a note of 258 be sounded simultaneously, as by 
means of two tuning forks, the resultant beats will be 258-256=2 
per second. This principle is of great value in exact tuning, since, 
if we have a standardized source of sound (i. e., a source whose 
vibration rate is exactly known), and a second source, whose vi- 
bration rate is near that of the first, but not definitely known, we 
can sound the two together, count the beats for a definite num- 



48 The actual tuning' of pianos merely approximates equal temperament, some strings 
having- approximately diatonic relationship to each other, while others are considerably 
farther out of "tune" than would be necessitated by the theoretical equal tempera- 
ment. For this reason, a piano composition is sometimes essentially different in 
effect in different keys, and pianists have not such keen pitch discrimination as those 
who have not played the piano. The fact that a piano does, not stay ' ' in tune ' ' 
longer than a few hours, adds to the mistuning and its effects. 



THE CRANIAL SENSES 89 

ber of seconds, and so determine the exact difference in vibration 
per second between the standard tone and the other tone. 

When the rate of beats approaches 30 per second, the beats 
fuse into a new tone, whose pitch corresponds to the rate of the 
fused beats, that is, to the difference in rate between the two 
sounds ; and this tone is therefore called a difference tone. 40 This 
difference tone, as can be demonstrated readily by drawing the 
curve of the combined sound wave, corresponds to a real periodic 
feature of the combined wave form, 50 and we can infer from this 
that any periodic (that is, regularly repeated) feature of a sound 
wave, if sufficiently emphatic (sufficiently intense), and of suffi- 
cient frequency, corresponds to a real simple tone in the total tone 
heard. 

In addition to primary beats and primary difference tones there 
are secondary beats and secondary difference tones, due to the fact 
that a tone of given rate beats not only with a tone a few vibra- 
tions slower or faster, but also with a tone a few vibrations slower 
or faster than its octave. For example, the note of 256 will 
give not only 2 beats per second with the note of 258 (pri- 
mary beat), but also 2 beats per second with the note of 514 (2x 
256 + 2). These secondary beats are relatively fainter than the 
primary. Manifestly, when the rate of the secondary beats is 
increased to 30 per second or more, these also will form a new 
tone (secondary difference tone). Beats and difference tones of 
the third, fourth and higher order have been reported by some ob- 
servers. 

Since most actual tones are complex, that is, contain many par- 
tials, the possibility of beats and difference tones between two 
such tones is complex. The fundamental of one may beat with the 
fundamental or higher partial of the other, or the higher partial 
of one may beat with a higher partial of the other. Even in the 



49Difference tones obtained by bowing" two strings of a violin simultaneously are 
knoAvn as Tartini's tones. 

soln the case of a difference tone, although there is, in the complex stimulation, a 
real periodicity corresponding to the pitch of the difference tone, the analysis of the 
complex wave gives no simple stimulus curve corresponding to it. The combination 
of two simple pendular air waves in these cases, gives a complex wave which is the 
stimulus of a complex note in which there are three simple tones. This fact constitutes 
one of the difficulties in the way of accepting the Helmholtz ' ' selective resonance ' ' 
theory of auditory stimulation. 



90 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

case of a single source of sound, such as a bell, or the human voice, 
the partials of which are not completely harmonic, these partials 
may beat with each other, producing the rapid ullulations which 
are peculiar to these sources. 

In musical practice, harmony and discord are of great im- 
portance. Two tones harmonize perfectly when the partials of 
both are harmonic, and every partial in one coincides with a par- 
tial of the other. In this case there are no beats. A tone will har- 
monize perfectly with its octave, or with any other note whose 
fundamental is an harmonic partial of the first note. The interval 
which ranks next in harmoniousness to the octave is the " per- 
fect fifth" of the diatonic scale, e.g., the interval c-g, or e-b, with 
ratio 2 :3. Next comes the major third, represented by c-e, f-a, or 
g-b, with ratio 4:5. In general, the smaller the ratio numbers of 
two notes, the more nearly perfect their harmony, as shown by the 
intervals just mentioned, and as may be further illustrated by 
comparing the perfect fifth c-g, with the fifth d-a, the ratios of 
which are 2:3 and 27:32 respectively. This rule does not hold in- 
variably, however, for the fourth, ratio 3 :4, is less harmonious than 
the major third, 4:5. 

Very imperfect harmony, in which there is not only failure of 
coincidence among the partials of the two (or more) tones, but also 
beats among the series of partials, is called discord. Less pro- 
nounced degrees of discord are called dissonances. Dissonances 
are not necessarily unpleasant, and modern music employs not 
only dissonances, but even discords, to produce its effects. Habit- 
formation has a large share in determining these effects. To a 
hearer accustomed to music in which few dissonances are em- 
ployed, dissonant music is highly disagreeable. But with con- 
tinued listening to such music, the hearer may come to prefer it to 
the more harmonious music. 

The auditory receptors are "hair cells": epithelial cells with 
cilia attached: located on the basilar membrane of the cochlea. 
Concerning the method of stimulation of these cells, a number of 
theories have been evolved, but none is conclusive. These recep- 
tors are arranged in two parallel series — a double row and a triple 
row — extending the length of the basilar membrane. From the 
psychological facts, we may tentatively infer that the stimulus 



THE CRANIAL SENSES 



91 



of a tone excites all the cells in a certain length of the receptor 
series, the length being the greater the lower the pitch; and that 
all the extents stimulated coincide at one end (the vestibular end) 
of the series. The highest perceptible tone, therefore, stimulates 
only the cells at the extreme end of the series; and all tones which 
excite the whole series of cells have a maximally low pitch. 

This hypothesis agrees with all the psychological facts, and 
with the few known physiological facts. 51 The destruction of re- 
ceptors at the vestibular end of the series produces deafness (ana- 
cusia) for high pitch, but not for low pitch. Presumably, in such 
cases, the low tones do not sound as low as they would if the whole 
receptorial series were intact, since the total number of receptors 



10 98 7 . 


3 


2 




^^ 










1 


1 



Fig. 11.- — Scheme of a complex tone. This scheme is drawn from Miller's measurements 
of the intensities of the partials of the organ-pipe tone, whose wave-form is represented in Figure 
10. The abscissae represent the pitches of the partials, and the ordinates represent the sums 
of the physical intensities. The scheme, therefore, represents the relative intensities of stimula- 
tion of the auditory receptors, from the vestibular end of this series (left) to the end of the 
stretch stimulated by the given note. 



stimulated is less. In inflammatory conditions of the middle ear, 
the apparent pitch of sounds may be changed in one ear as com- 
pared with the other (a condition known as diplacusia binauralis 
dysharmonia) : the change in at least one carefully observed case 
having been approximately a semi-tone (ratio 15:16.) In such a 
case it is possible that the change in the density of the fluid sur- 

siThe existence of "tone-gaps" and "tone-islands" might be supposed to militate 
against this theory; but these are pretty clearly due to abnormal conditions of the 
mechanism for transmitting sounds to the internal ear. In the case of a tone-gap the 
patient is anacusie (deaf) to sounds of a certain range of pitch, although sensitive 
to sounds above and below the range. In the case of a tone-island, two such gaps 
enclose a short sensitive range. 



92 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

rounding the basilar membrane changes the length of the portion 
of the receptor series excited by a stimulus of a given frequency. 

The structural characteristic of the cochlea which appears to 
support the extensity theory consists in the form of the tectorial 
membrane, which overlies the receptors. This membrane increases 
in width and thickness from the end nearest the middle ear to the 
end nearer the vertex of the cochlea. While the structure and at- 
tachments of this membrane are not such as would lend themselves 
to "resonance" or sympathetic vibration, the progressive increase 
in inertia of the membrane from one end to the other does suggest 
the functions demanded by the extensity theory. The parts of 
the membrane which could be set in motion by Avaves of high fre- 
quency would also be set in motion by waves of slower frequency. 

On the psychological side, we have the following facts which 
support our hypothesis: 

First: high pitched tones are heard as less extensive, 
smaller, than low pitched tones. If one listens to tones of varying 
pitch, with as little prejudice as possible for the common termi- 
nology, one finds that the bass notes are describable as large, 
bulky: the treble notes fine, thin, and so on. Obviously, these are 
metaphorical terms, used to convey the similarity between the 
pitch variation and the variation in size of tactual and visual ob- 
jects. 52 

Second: the apparent pitch of any complex tone is the pitch 
of its lowest partial. The reason for this can be seen by referring 
to Fig. 11 much more easily than it can be explained in words. 

Third : a loud low tone will drown out a faint high tone, but a 
high tone, however loud, will not interfere with the perception of 
a faint low one (provided "beats" and other secondary effects 
are excluded). 

Fourth: there is an essential difference between the "musical 
ear" and the "unmusical ear." An individual who has an "un- 
musical ear" judges pitch differences in a rough way, as if mere 
gross sizes of objects are directly compared. On the other hand, 



ssThe origin of the terms "high" and "low" as applied to pitch is obscure, but 
probably comes from the observed behavior of the throat in singing. The Greeks 
used the two terms in exactly the opposite way, the notes of the long strings of the harp 
being "high," and the notes of the short strings "low." Apparently this designa- 
tion was due to the position of the hand in plucking the strings. 



THE CRANIAL SENSES Vd 

tlie person with a musical ear judges in a more exact way, as if 
he noted the point to which (as represented in the scheme) each 
tone extends. In extreme development of the "musical ear", it 
reaches what is called absolute pitch, which is the ability to recog- 
nize at any time the approximate pitch of any note heard, regard- 
less of the relation to other notes. In cases of ordinary musical 
proficiency, it is possible to tell whether a note sounded is of 
the pitch of a note heard from several minutes to several hours 
before, or whether the two differ even slightly. 

Anacusia for high pitches, or reduced sensitivity to high 
pitches, with little apparent effect on the audition for low pitch, 
is of frequent occurrence. Individuals suffering from the defect 
may be "normal" up to 1,000 vibrations per second, and may even 
be hypersensitive to tones in the lower part of the usual range 
(below 128 v.s., for example) ; yet they have difficulty in under- 
standing words, and especially whispers, because the discrimina- 
tion of consonants depends upon the hearing of the high partials 
in the vocal sounds. Apparent dullness of children in school is 
sometimes due to this cause, and inability to understand whispers 
easily is always a sufficient reason for having the hearing tested 
by a psychologist. A child recently examined in the Johns Hop- 
kins Psychological Laboratory had been pronounced "feeble- 
minded" by his teacher, and "normal" in hearing by an ear spe- 
cialist; but was found, on careful test, to be seriously defective 
in the upper auditory range, and mentally above normal. 53 

In some cases of anacusia for high pitches, the sensitivity for 
low pitches is even greater than that of the "normal" ear. These 
cases are not helped by the microphone devices, now much used 
by deaf people, because these devices intensify the low pitched 
notes relatively more than the high pitched, and so increase the 
difficulty of hearing language. In another type of deafness, in 
which the anacusia extends also to low pitches, these devices are 
beneficial. A third type of deafness, in which there is anacusia 
for low pitched tones, with less or none for the higher pitches, 
might be supposed to exist, on the basis of some theories of au- 
dition. 



sslt should be explained that the reason some ear specialists do not detect such con- 
ditions is that they have no instruments for the purpose, and in many cases are not in- 
terested in the condition, as nothing- can be done for it therapeutically. 



CHAPTER IV 

THE SOMATIC, VISCERAL AND LABYRINTHINE SENSES 

§1. The dermal senses. 

The modal senses of touch, pressure, warmth, cold, pain and 
tickle have bipolar nerve cells as receptors. The cell bodies of 
these receptors lie either in the spinal ganglia, close to the spinal 
cord, or in certain ganglia of the head, adjacent to the brain stem; 
and the dendrites of the receptors terminate in the skin, the sub- 
cutaneous tissues, and the mucous membrane of the mouth, the 
upper part of the gullet, and the anus. 

Each of these senses apparently functions for sense data of one 
quality only, just as does the auditory sense. 

The physiological separation of the tactual, rhigotic, thalpotic 
and algetic senses is sharply shown by certain cases of disease or 
injury of the spinal cord or brain stem. In some such cases, der- 
mal areas are found which are totally insensitive to pain, although 
sensitive in the other three modes. In other cases, thalpotic sensi- 
tivity alone is lost. In other cases rhigotic sensitivity alone may 
be lost. In various cases, dermal areas are found in which two 
forms of sensitivity are lost, and the other two retained. 

Tickle 

The adequate stimulus for tickle is very light contact with the 
skin (or mucous membrane) or with hairs, and is intensified by 
movement of the contact over the surface. The term tickle is here 
applied to sense data of a distinct quality, and does not refer to 
the profound organic processes and experiences which are set up 
by stimulation of the subcutaneous tissues of the trunk, as by 
pressure in the region of the ribs or abdomen. 

The reaction set up by the tickle-stimulus may be violent as 
compared with the stimulus intensity, and usually provokes the 
movement of rubbing the part of the skin tickled. It has been 

94 



THE SOMATIC, VISCERAL AND LABYRINTHINE SENSES 95 

suggested that the development of this reaction has been of serv- 
ice to man as a protection against insects, since the stimulation 
produced by an insect brings about the reaction which would 
destroy it or brush it away. Tickle is exclusively a characteristic 
of the body itself, and is never perceived as in an external object: 
tickle-perception is strictly a form of auto-perception. Very little 
further can be said about tickle at present, since in investigation 
of dermal sensitivity it has usually been neglected, or confused 
with touch. 

Epicritic and Protopathic Sensitivity 
Early investigations of touch, pressure, warmth and cold re- 
sulted in serious confusion, which has been cleared up by the clini- 
cal and experimental work of Henry Head and his co-workers. It 
is now known that there are two sets of sensory mechanisms, one 
the epicritic, functioning for the perception of touch or contact, 
mild warmth, (from 37° to 45° C.), 54 and mild cold, (from 37° to 
20° C.) : the other, the protopathic, functioning for pressure, pain 
and the higher intensities of heat and cold, (above 45° and below 
20° C). In certain cases of disease or injury of the peripheral 
nerves, protopathic sensitivity alone, or epicritic alone, has been 
found on certain areas of the skin, and thus each has been studied 
in isolation. Some areas, such as the glans penis of the male (and 
apparently the linings of the sinuses, or cavities in the skull bone 
which connect with the nasal cavities) normally possess only pro- 
topathic sensitivity. 

Protopathic sensitivity is autoceptive. Through its mechan- 
ism, when acting alone, we perceive pressure, pain, heat and cold, 
as conditions of the skin or mucous membrane themselves, never 
as properties of external objects. Epicritic sensitivity, on the 
other hand, is Interoceptive : mild warmth and coolness and the 
tactual quality (contact) are felt as properties of objects touching 
the body surface. When both systems are active together, on the 
same area, the protopathic qualities may be perceived as external, 
or the epicritic as organic. 

Protopathic sensitivity is definitely localized. Appropriate 
stimulation at certain points in the skin produces perception of 

^Assuming the temperature zero of the body to be at 37°. 



96 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

heat ; at other points, cold ; at others, pressure ; and at others, pain. 
At other points no response can be obtained. It is assumed, there- 
fore, that there are specialized receptors for each of these sense- 
data. Epicritic sensitivity, on the other hand, is only in part lo- 
calized. Stimulation of any point on the skin, by means of a stiff 
bristle, will produce touch, although the sensitivity is greater at 
some points than at others. Epicritic warmth and coolness seems 
to be localized in a general way Avithin small areas. Within one 
of these ''warmth areas" there are always to be found points at 
which the epicritic warmth can be aroused, although at times there 
may be other points at which it can not be aroused. Similarly, 
there are cool areas, within which the epicritic coolness can be 
felt always at some points, although perhaps not at others. There 
are other areas within which the epicritic cool never can be felt, 
and areas which are immune to warmth. The exact localization 
of the sensitive points within the areas varies from time to time, 
however, so that we can speak of the localization as areal only, 
not as punctuate. 

In contrast with the actual localization of epicritic and proto- 
pathic sensitivity, the perception of locality is relatively acute 
through epicritic sensitivity, and relatively vague and inaccurate 
through protopathic. On areas supplied with protopathic sensi- 
tivity only, the location of stimulated areas can be identified only 
in a vague or general way. 

Since there is no epicritic pain to be confused with the proto- 
pathic pain, the punctuate localization of pain sensitivity can be 
demonstrated on the normal skin, by stimulating with a fine needle. 
At some points light pricking with the needle point gives distinctly 
the pain quality: at others the needle can be thrust into the skin 
without any pain. 

Prior to Head's work, it was believed that warmth and cool 
sensitivity were localized punctuately, just as pain was found to 
be. This belief was due in part to the ignorance of the distinction 
between protopathic and epicritic sensitivity, and in part to faulty 
methods of research. Especially careful technique is needed in 
conducting research upon the dermal senses, because they are 
maximally subject to "suggestion" effects. That is to say: Re- 
actions primarily initiated through these receptors may be influ- 



THE SOMATIC, VISCERAL AND LABYRINTHINE SENSES 97 

enced profoundly by the stimulation of other senses, and by idea- 
tional reactions occurring at the same time, or just preceding. An 
instance of this "suggestion" effect which most men have experi- 
enced is the "electric" effect of a lock of a girl's hair brushing 
lightly against his temple : far different from a mechanically simi- 
lar stimulation produced by a tuft of cotton. 

In spite of the functional difference between the epicritic and 
protopathic sensitivities, it is not necessary to suppose that there 
are four temperature senses. The differentiation between warmth- 
sensitivity and heat-sensitivity, and between cool-sensitivity and 
cold-sensitivity is to a large extent peripheral. In diseases of the 
spinal cord and of the brain, it is found that if warmth-sensitivity 
is affected, heat-sensitivity is also affected; and that cool-sensi- 
tivity and cold-sensitivity also are affected alike. Either of the 
thermal senses may be lost, on certain areas, through injury to the 
cord or brain, without affecting touch and pressure, or pain; and 
similarly, either of these latter may also be disturbed. The whole 
matter of the relationships of these senses is exceedingly com- 
plicated, and no final conclusion is yet possible. 

Thermal Stimulation 

The normal rhigotic stimulation is the loss of heat from the 
skin, and the normal thalpotic stimulation is the conduction of 
heat to the skin. Heat, physically considered, is molecular vibra- 
tion, and may be conducted by transference of the vibrations from 
molecule to molecule. This sort of conduction is supposed to oc- 
cur when a hot or a cold object is applied to the skin. "Radiant 
heat", which may become a stimulus when a hot object is placed 
near the skin, is not properly speaking "heat" at all, until it 
strikes the skin. The molecular vibrations of the hot object set 
up ether vibrations mostly of wave lengths greater than that 
of the visible spectrum, and these ether vibrations, transmitted 
to the skin, excite in the skin "heat", i. e., molecular vibrations of 
a certain sort. Similarly, when ice is brought near the skin, ether 
waves, caused by the heat in the skin, radiate to the ice, and are 
there transformed into heat. 

Heat as such is not a sensorv stimulus under ordinarv condi- 



98 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

tions. The conduction of heat to the skin, or the checking of the 
conduction away, may be the stimulus for ' ' warmth ' ', and the con- 
duction away in excess of a certain rate, is the stimulus for 
"cold". 

The rate of conduction in either direction required to stimulate 
the receptors is variable, being subject to adaptation. Under nor- 
mal conditions, there is a physiological zero for any given point 
on the skin, and the cooling of the skin below that temperature, 
if the cooling is sufficiently rapid, produces rhigosis; the raising 
of the temperature above the physiological zero-point produces 
thalposis. This physiological zero is usually assumed to be about 
37° C. (98° F.), but is subject to adaptation, and differs in differ- 
ent parts of the body at the same time. 

If two dishes of water are provided, one feeling distinctly cool, 
the other icy cold, to the finger; and if the finger is kept in the 
colder water for some seconds, and then transferred to the less 
cold, the latter will feel warm. Conversely, by adaptation to hot 
water, water which is normally warm will feel cold. Adaptation 
may be carried even to dangerous extremes. In one case, under 
a physician's order, a patient's hand was kept for several hours 
in a bowl of water to be maintained at a temperature "as high 
as the patient found comfortable". The temperature was slowly 
raised during this period, and the skin scalded from the patient's 
hand without the least discomfort. A frog may be killed by heat, 
if placed in cold water which is subsequently raised in temper- 
ature at a slow rate, without the frog's showing the least evidence 
of unpleasant stimulation. 

Hair Sensitivity 

Although the skin and hair bulbs in general function similarly 
in tickle and touch perception, there is a difference in their neural 
mechanisms, and in certain cases of nervous disease, trichesthesis 
may be lost without disturbance of skin touch, and converse cases 
have also been reported. The receptors ending in the hair bulb 
may be stimulated by very light contact with the hair, which acts 
as a lever to increase the pressure in the bulb. 



the somatic, visceral and labyrinthine senses 99 

Fusions of Dermal Sense Data 

It has been claimed that the different modes of dermal sensi- 
tivity in reality form a single sense, since the data of these senses 
fuse with one another, just as do the four tastes with each other. 
It is true that fusions of touch and warmth, touch and cold, are 
common occurrences. Tickle and heat also fuse in the form of 
"itch". The two thermal, qualities, however, never fuse with each 
other : there is no such thing as cold-warmth. Although the theory 
that heat is a fusion of cold and warmth was seriously maintained 
some years ago, the grounds for the theory have been swept away 
by Head's work. Since these are manifestly of different modes, 
the fusion of touch with each of them does not prove that touch 
belongs to the mode of either. For the present, therefore, it is best 
to consider the dermal sense as being six distinct modes. 

Inadequate Stimulation of the Dermal Senses 

It is said that a sudden hot stimulus may excite the cold (proto- 
pathic) receptors, giving rise to the "paradoxical cold" percep- 
tion. This perception is often caused by plunging the hand or 
foot into a tub of hot water, not previously known to be hot. 
Whether this is really a case of inadequate stimulation, or a case 
of failure to recognize a sensory quality, is open to discussion. 
Intensive heat is usually fused with some degree of pain, and the 
occurrence of the heat without the pain, in the first moments of 
stimulation, makes the recognition more difficult. It is interesting 
to note that savages who are totally unfamiliar with ice and snow, 
report on first contact, that it "burns" them, although there is no 
evidence for inadequate stimulation of the heat receptors in such 
cases. 

Tickle may be caused by physiological conditions of the skin 
without contact. Heat also may be physiologically stimulated. 
The occurrence of the two fused in itch has been already noted. 
Touch, tickle, pressure and pain may be excited by electrical stim- 
ulation. 

§2. Palmesthesis 

Whether there are special receptors for palmesthesis (the vi- 
bration sense) or whether receptors for other somatic senses also 



100 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

function palmesthetically, cannot be determined at present. Vi- 
bration can be perceived apparently through receptors terminating 
in the skin, subcutaneous tissue, and the bones, or membrane cov- 
ering the bones. The muscles also may be palmesthetically sensi- 
tive, but this is not certain. The stimuli are molar vibrations of 
the same type as the auditory stimuli, of a frequency range which 
overlaps the audible range, beginning somewhat lower, but not 
extending as high as the latter. The exact limits have not been 
determined. 

In testing palmesthetic sensitivity, it is necessary to take pre- 
cautions that the stimulation shall not be transmitted to the audi- 
tory mechanism, either through the air or through the bones of 
the skeleton. Confusion of auditory and palmesthetic qualities 
may easily occur; but the separation of the senses is certain. To- 
tally acusic individuals are able to perceive vibration, through the 
fingers or other parts of the body, and to distinguish the extensity 
(rate) of these vibrations. Deaf persons may derive satisfaction 
from palmesthetic stimulation obtained by touching a violin or 
other instrument while it is played, and may be able to recognize 
and distinguish musical compositions palmesthetically. It is prob- 
able that in such discrimination, the rhythm of the stimulus is at 
least as important as the extensity (" pitch") differences. 

Palmesthesis has been frequently classified under touch or 
pressure, and vibration as perceived supposed to be a series of 
touches. That this assumption is not correct is evident from the 
facts that: (1) palmesthesis may be present on areas of the body 
from which touch and pressure have been lost through disease 
of portions of the nervous system: (2) palmesthesis is present in 
parts of the body (i. e., the bones) in which neither touch nor pres- 
sure is present even in normal conditions: and (3) vibration can be 
distinctly perceived at rates of vibration far above the rate at 
which touch stimuli fuse into continuous touch (analogous to the 
fusing of flashes of light, at rates above the critical frequency). 

The most convenient means for the demonstration of palmes- 
thesis is by setting a light-weight tuning fork in vibration at low 
amplitude, and pressing the end of the fork-stem on the skin of the 
hand or foot, selecting the fleshiest parts to avoid transmission to 



THE SOMATIC, VISCERAL AND LABYRINTHINE SENSES 101 

the bone. Forks of vibration rates below 500 v. s. are most satis- 
factory. 

§3. The sexual sense. 

Receptors terminating in the glans penis of the male, and in 
both external genitalia and vagina of the female, function in the 
perception of a sense datum whose stimulation is physical con- 
tact, but whose quality seems to be distinctly different from that 
of dermal touch. The conclusion that the sense is a specific one 
is supported by the claims of some histologists that the genital re- 
ceptors differ from the termination of receptors for dermal touch. 
This claim is, however, not undisputed. Observation is rendered 
difficult by the fact that the reactions caused by genital stimula- 
tion produce organic sense data in other parts of the body, which 
are both extensive and intense, and which conjoin with the genital 
data so intimately as to make qualitative discrimination difficult. 
It is possible tliat the so-called genital quality, if entirely ab- 
stracted from these organic qualities, is nothing more than ordi- 
nary protopathic pressure. But the greater probability is that al- 
though more closely akin to protopathic than to epicritic quality, 
the sexual quality is sui generis. Whether the quality in the male 
is different from that in the female is a question to which the an- 
swer is at present conjectural. 

§4. Kinesthesis. 

Kinesthesis, or the awareness of movement, is a complex 
process depending peripherally upon receptors in the striped 
muscles, in the tendons, the joint surfaces, and the joint capsules. 
The dermal sensitivity also cooperates with kinesthetic sensitivity, 
since movement of the parts of the body, by changing tensions 
on skin and subcutaneous tissues, stimulates receptors there. But 
the role of dermal and subdermal sensitivity is adventitious, and 
not essential, to kinesthesis. 

The terms proprioception and proprioceptive are sometimes 
applied to kinesthetic sensitivity and the kinesthetic mechanism 
alone, since this form of sensitivity is sometimes literally percep- 
tion of one's self, and not of external objects. As we have seen al- 
ready, tickle, pressure, pain and protopathic heat and cold are 
as really proprioceptive as is kinesthesis ; and the same is true of 



102 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

the visceral sensitivity (cenesthesis) ; whereas on the other hand, 
the kinesthetic mechanism has also certain non-proprioceptive 
functions, as described below. The term proprioceptive is there- 
fore an unfortunately confusing one for psychology, and its use is 
not to be recommended. 

It is not certain that there is more than one kinesthetic quality. 
Movement is the real datum perceived, and the various perceptible 
movements are complexes of different intensities and extensities, 
but it is not obvious that they are complexes of different qualities. 

Evidence of the function of the joint surface in kinesthesis is 
found in the fact that movement of an arm or leg is more ac- 
curately perceived when the moving, joint surfaces are pressed to- 
gether, than when they are pulled apart. The functioning of the 
muscles might be inferred from the rich supply of afferent nerve 
fibers which connect with the muscles, and the inference is con- 
clusively corroborated by the ataxia which follows interruption of 
these fibers. Ataxia is the condition in which movements of the 
limbs or trunk are poorly coordinated and are perceived with in- 
accuracy. 

The kinesthetic mechanism seems to have other functions in ad- 
dition to kinesthesis. One of these, which is distinctly not proprio- 
ceptive, is : the perception of resistance offered by external objects. 
This function, whether exercised in pressure against an object, 
or in lifting a weight, is an important aid in our acquisition of 
knowledge of the outside world. Kinesthesis is also an essential 
means for the development of the perception of space relations, 
so that its " proprioceptive " function is in many respects a minor 
one. 

Other functions of the muscular division of kinesthesis are the 
experience of strain and fatigue, with their after-effects of relaxa- 
tion and relief. These, while functions of the mechanism which 
is conveniently designated as kinesthetic, are strictly cenesthetic 
("proprioceptive" in the legitimate sense of the word), and will 
be described under organic sensitivity. 

§5. Bodily feelings. 

The data of the organic senses, although complexes of senti- 
enda, are commonly called feelings. This term was formerly ap- 



THE SOMATIC, VISCERAL AND LABYRINTHINE SENSES 103 

plied to tactual, thermal and kinesthetic data, and is very fre- 
quently applied to tickle and pain, since these are truly organic. 
We shall use the word "feeling" here as strictly synonymous with 
organic sense data, that is to say, as designating perceptible con- 
ditions of the body or organism itself. 

Organic sensitivity probably includes many different modes, 
but their discrimination is exceedingly difficult. Strictly speaking, 
the sexual sense; the dermal pain and tickle senses; and the proto- 
pathic pressure, heat and cold senses, are organic senses ; and our 
inclusion of these under different heads is to be understood as a 
mere deference to custom, defensible only on didactic grounds. 

The Pain Sense 

The so-called dermal pain sense is merely one detail of a more 
general pain sense, which has receptors terminating in almost all 
tissues of the body. There are apparently a number — perhaps a 
large number — of pain qualities, including the quality which is 
observed on the skin, and the ache which subcutaneous tissues 
and the teeth sometimes have. The peculiar "cutting" or "stick- 
ing" pain referred to the heart, the tearing pain which sometimes 
follows the drinking of cold water in the morning, the gripes of 
intestinal colic, the pains of blinding light, intense noises, and over- 
stimulation of the genital sense, are either distinct qualities or 
are complexes embodying distinct qualities other than the com- 
mon ache and pain. Many complex pains include data of other 
modes — heat, cold, pressure, kinesthetic, and organic data. In 
some cases, the pain is so intimately combined with another qual- 
ity, that analysis of the former is difficult. This is the case with 
"blinding pain" of the retina, which in the normal eye occurs only 
fused with intense light. In certain cases where vision has been 
completely lost, however, the characteristic "blinding" pain alone 
is produced by intense light stimulation. 

The relation between heat and certain forms of pain is peculiar, 
the two qualities sometimes being difficult to distinguish. The 
boring of a dentist's drill into a sensitive tooth produces an in- 
tense feeling which is perhaps a fusion of heat and pain; or else 
is a quality of pain hardly distinguishable from heat. Cold, on the 



104 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

other hand, is often qualitatively confused with ache, perhaps be- 
cause cold-stimulation frequently produces ache. I have sug- 
gested earlier the possibility that pain and ache are really high in- 
tensities of heat and cold respectively, and this suggestion is by 
no means an irrelevant one. 

Pain is perceived in general when the response of any receptor 
to an adequate or inadequate stimulus is sufficiently intense. It 
would appear, therefore, that there is no specific receptor for pain. 
It is reported by various observers, however, that at certain points 
in the skin and conjunctiva, light stimulation, by mechanical pres- 
sure, usually produces pain, but no other sense quality. These 
observations may be erroneous. It is not improbable that these 
responses in the skin are due to receptors which also function for 
the tickle sense and in the conjunctiva to touch receptors, the 
limits between the stimulation which produces tactual quality and 
that which produces pain being so small as to be overlooked. But 
if it is true that a limited group of receptors are actually so consti- 
tuted that any response thereof is a pain response, this does not 
conflict with the general fact that pain perception is the function of 
receptors of all types. 

Over against the receptors which perhaps respond to pain only, 
we must set receptors, such as those for epicritic warmth, which 
cannot be overstimulated. Application of intense adequate stimuli, 
or inadequate stimuli, apparently never produces intense warmth 
(heat), but these receptors cease to function entirely under such 
stimulation. 

The analysis of pain sensitivity is complicated by the fact that 
analgesia of bodily areas, dermal and internal, may exist without 
anesthesia for any other qualities, and the converse condition also 
occurs. This, presumably, is due to the fact that the routes of 
conduction in the spinal cord and brain-stem for the neural im- 
pulse involved in pain perception are separate from those for other 
afferent impulses from the same body areas, and the interruption 
of one of these routes may occur through disease or injury, with- 
out affecting the other. The whole matter of pain sensitivity is 
obscure, and final conclusions must wait upon further experimental 
and clinical work, for which the discoveries of Head have pre- 



THE SOMATIC, VISCERAL AND LABYRINTHINE SENSES 105 

pared the way. The literature of the subject for the period pre- 
ceding Head is full of confusing and contradictory observations, 
on which it is now necessary to look with considerable skepticism. 

Alimentary Sensitivity 

Aside from the gustatory and dermal sensitivity regionally con- 
nected with the mucous membrane of the mouth and anus, the 
alimentary canal has several forms of sensitivity. Of these the 
most conspicuous are hunger and thirst. Thirst is a condition of 
the mucous membrane of the pharynx and the upper part of the 
gullet. Certain receptors whose dendrites terminate in this region 
are probably stimulated by the reduction of the w T ater content of 
adjacent epithelial cells. When the water content of the organ- 
ism needs replenishing, these cells are affected early, and thirst 
is experienced; and also reactions effective in obtaining renewed 
water supply are brought about. That the thirst, while normally 
an index of a general systemic need, is itself a local condition, is 
demonstrated by the fact that local dryness produced by dry or 
dusty air, or by the application of chemicals (such as salt) which 
extract water from the tissues, when the general system is ade- 
quately supplied with water, gives rise to thirst which may be 
removed by the local wetting of the mucous membrane. 

Conditions of other tissues similar to thirst are apparently set 
up in advanced stages of water deprivation, and in febrile dis- 
eases. These conditions, however, are not called thirst. 

Hunger is apparently a condition of the mucous membrane of 
the stomach, although the details of stimulation of the receptors 
are not understood. Hunger normally occurs only when the 
stomach is empty, (although it may occur when the stomach is 
full) and it has been found by Cannon, Carlson and others, that 
in some persons the hunger increases and decreases rhythmically 
with periods of a number of seconds; and that this periodic fluctua- 
tion of the hunger is approximately synchronous with tonic con- 
traction and relaxation of the empty stomach. Further details 
concerning hunger will be given in Chapter XV. 

Nausea is a common stomach condition which leads in some 
cases to stomach contraction with relaxation of the gullet. Nausea 



106 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

may be induced in various ways; by direct stimulation of 
the stomach, by stimulation of the root of the tongue or of the 
region of the juncture of the gullet and pharynx, and by stimula- 
tion of the semicircular canals of the head. The actual stimulus, 
in other words, is produced in the stomach as a result of nerve 
currents whose primary origin may be various. The "settled" 
condition of the stomach, after vomiting has occurred, is appar- 
ently as distinctly perceptible a condition as is the preceding- 
nausea. 

Appetite for food is said to involve, in addition to desire, a spe- 
cific "food-feeling," distinct from hunger. This feeling occurs, 
even when one is not hungry, in the smelling or tasting of good 
food; but it is neither the odor nor the taste. When appetite is 
aroused, and food taken into the stomach, a distinctly different 
feeling of satisfaction is usually obtained. These feelings are com- 
monly accompanied by pleasure, but are distinct from the pleasure. 

Fullness of the stomach, and fullness of the small intestines, 
are distincly perceptible, and definitely due to a certain degree of 
stretching of the coats of the stomach and intestines. Emptiness 
is an equally perceptible condition, and relief after fullness and 
after emptiness is also recognizable. The fullness of the rectum, 
which is the usual sign of the need for defecation, and the relief 
which follows normal defecation are apparently qualitatively dis- 
tinct from the fullness and relief of the stomach and small intes- 
tines. 

Pain may be aroused in any part of the alimentary tract, but 
apparently only by intense muscular contraction, or chemical 
stimuli. Cutting and other mechanical injury is without effect, 
although the peritoneum and pleurae which cover the stomach, 
intestines and other entrails, and line the abdominal and thoracic 
cavities, are extremely sensitive to mechanical injury. Touch and 
pressure sensitivity are absent from the stomach, and warmth can- 
not be stimulated in that organ except by chemical means (alcohol, 
for example), not -by thermal stimuli. 55 



ssThe heat felt after drinking too hot a liquid comes not from the stomach, but from 
the peritoneum, being transmitted through the stomach wall without affecting it sen- 
sorily. The mouth and upper part of the gullet, of course, are sensitive to thermal 
stimulation. 



visceral and labyrinthine senses 107 

Genito-Urinary Feelings 

Fullness of the bladder, and relief after urination, are data of 
distinct qualities. The contraction of the urethra and sphincter 
muscles of the bladder are also distinctly perceptible. Intense 
pain may be aroused in these organs and in the kidneys, by me- 
chanical and chemical stimulation. 

In addition to the specific genital quality which has been men- 
tioned under another heading, there are intense feelings, appar- 
ently of complex quality, which are localized in the external and 
internal genitalia. Sexual appetite and sexual satiety of a local- 
ized sort are among them. These are so conjoined with pleasure 
and other general bodily feelings that the clear discrimination of 
the specific sex feelings from the total cenesthesis is almost im- 
possible. 

Cardiovascular and Respiratory Feelings 

The normal contractions of the heart are perceptible, but 
whether this perception is actually cardiac or peritoneal cannot 
be decided. Intense contractions are distinct, and the sudden 
checking of the heart produces a perception of an intense, but in- 
describable sense quality. Cardiac pain is usually of the " sharp" 
variety, although literal "heart-ache" is not impossible. The con- 
traction and relaxation of the muscular coats of the blood vessels 
contribute a vast mass of sensory data, which is of considerable 
importance for our conscious experiences. The "feeling of excite- 
ment" and the "feeling of depression" are very probably condi- 
tions of the general vascular system (heart and blood vessels). 
The sudden flushing or blushing of the skin, due to relaxation of 
the capillaries, is as perceptible organically to the blushing indi- 
vidual as it is visually to the spectators. 

The choking feeling in the throat frequent in rage, fear and 
sudden joy may also be classed as cardiovascular. It is supposed 
to be due in part to the swelling of the thyroid gland by increased 
blood supply. 

In addition to the muscular feelings associated with the proc- 
ess of respiration, there are certain feelings dependent upon the 
process, which, however, may be really vascular rather than 



108 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

strictly respiratory. The feeling of stuffiness in a close room is 
distinguished from the thermal and olfactory sense data accom- 
panying it. The feeling of suffocation which follows prolonged 
holding of the breath is perhaps qualitatively identical with 
' ' stuffiness.' ' The feeling of respiratory relief which is produced 
by the resumption of breathing, and also by the breathing of 
"fresh" air after "close" air, is distinguishable from other relief 
feelings. 

Vestibular and Ampullar Senses 

There are two groups of receptors, both hair-cells similar to 
those of the auditory sense, located in the vestibule of the inner 
ear, and the ampullae of the semicircular canals, which connect 
with the vestibule. The vestibular receptors have been supposed 
to have a function in noise perception ; but it is noAV known that 
they, as well as the ampullar receptors, have no auditory function 
whatever. Much speculation has been indulged in regarding the 
function of these receptors. They have been supposed to be organs 
for the direct perception of motion, but this supposition has no 
foundation. It is not even certain that these receptors have any 
sensory function at all, although they are commonly referred to 
as "sense organs," and in the opinion of the author, are organic 
sensory mechanisms. 56 

The primary function of the vestibular and ampullar mechan- 
ism is one with which sense perception is not necessarily con- 
nected, namely, the control of bodily movements and of eye move- 
ments. The adequate stimulus for the ampullar mechanism is 
movement of rotation of the head. The adequate stimulus for the 
vestibular organ is change of position of the head, either rotary 
or linear. These stimulations reflexly produce change in the tonus 
of various groups of skeletal muscles: changes which are demon- 
strated in bending and twisting of the body, and in eye-nystag- 
mus, and which assist in compensating for the head movements 
and thus in maintaining equilibrium, and in facilitating visual co- 
ordination. 



56Not even the physiologists who designate the vestibular and ampullar receptors as 
"sense organs" assume a sensory function, as psychologists use the term l( sensory", 
namely, as applying to perceptual processes or mechanisms. The physiologists use 
"sensory" as equivalent to "afferent", with no implication as to experience. 



THE SOMATIC, VISCERAL AND LABYRINTHINE SENSES 109 

As a result of these changes in the striped muscles, movements, 
both real and illusory, are perceived. Along with the striped 
muscles, the visceral muscles are affected, one indirect effect of 
strong stimulation of the ampullar and vestibular receptors being 
nausea. 

In addition to the illusion of motion and the nausea, produced 
indirectly by such stimuli as rotation, when sufficiently violent and 
prolonged, there is a feeling of a peculiar quality, localized vaguely 
in the head, which is probably due to a direct sensory function of 
the vestibular or ampullar apparatus, or both. The term "ver- 
tigo ' ' is unfortunately used to cover this feeling, the illusory move- 
ment and the nausea, indiscriminately. "We might perhaps call 
this feeling giddiness, if we should refuse to apply this term to 
the other two phenomena confused with it under the term vertigo. 

Fatigue 

The term fatigue is used to indicate three different phenomena: 
(1) The exhaustion of an organism, or part of an organism, and 
the consequent impairing of its functional efficiency. Such exhaus- 
tion is usually brought about by the continuation of the function 
itself. Thus, if a weight be lifted repeatedly as rapidly as pos- 
sible, by means of a finger, the height and frequency of the move- 
ment soon begins to diminish, and finally the movement becomes 
almost impossible. 57 The mechanism, in short, has become ex- 
hausted. (2) The term is also applied to adaptation processes, 
such as those occurring in vision, which are probably not exhaus- 
tion effects at all. (3) Fatigue, in the sense in which we shall 
use it here, is a condition of the striped muscles, apparently due 
to the presence of certain toxic substances, of which the most im- 
portant is lactic acid (or certain lactates), with possibly some ef- 
fect of carbon dioxid and acid calcium phosphate: substances 
which are produced by muscular activity. It is also claimed that 
other toxic substances produced in the muscles are effective. These 

57This is the ergograpliic test. The exhaustion is principally in the central nerve 
cells (in brain and cord), and in the juncture between efferent nerve fibers and muscle 
fibers. The afferent and efferent nerve cells can practically not be exhausted, and in 
the ergographic test, the muscles themselves have suffered comparatively little loss of 
contractile ability. 



110 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

substances are carried by the blood stream throughout the organ- 
ism, and produce their effects, therefore, not only in the muscles 
where they originate, but in the musculature generally. On this 
account, work done by a limited group of muscles, for example, 
by the legs in working a pedal-machine, produces not merely 
fatigue of that muscle group, but of the whole muscular system. 

The toxic fatigue substances probably act as stimuli to the 
receiptors terminating in the striped muscles. This part of the so- 
called "kinesthetic" sensory mechanism has accordingly a range 
of non-kinesthetic organic functions even greater than that which 
we have above indicated. The toxic substances are normally de- 
stroyed by oxidation in the blood, although in extreme fatigue 
they may be excreted unoxidized by the kidneys and sweat glands. 
Epinephrin, or adrenin, which is secreted into the blood by the 
adrenal glands, apparently is capable of neutralizing the effect of 
these substances, or of hastening their oxidation, and so is a power- 
ful agent in the counteraction of fatigue. The phenomenon of 
"second wind" is now believed to be largely due to the increased 
production of adrenin under conditions of extreme fatigue and 
emotional excitement. The condition sometimes described by the 
misleading term mental fatigue is usually a condition of exhaus- 
tion or toxic poisoning of the nervous apparatus, occurring with- 
out a large amount of true fatigue. Some actual fatigue, espe- 
cially of the vocal muscles, frequently occurs in "mental fatigue," 
but the most characteristic feelings in such conditions are depres- 
sion and excitation. In cases of decided real fatigue, the so-called 
"mental fatigue" effects may also be present, and may be due 
principally to action on the nerve cells by the lactic acid and other 
substances which produce the muscular fatigue feeling. 

If the term "fatigue" is to be retained in application to ex- 
haustion and toxic effects in the central nervous system, and to 
the effects of their condition in psychological efficiency, it would 
be better to distinguish them as "central fatigue" and "central 
fatigue" effects, from the condition of fatigue-feelings to which 
the term muscular fatigue may be applied. Central fatigue must, 
in the future, receive a large amount of attention from experi- 
mental psychology, on account of the practical importance of the 



VISCERAL AND LABYRINTHINE SENSES 111 

topic, in connection with school, commercial and industrial opera- 
tions. 

Pleasantness and Unpleasantness 

These feelings have been the subject of much controversy, and 
many hypotheses concerning them have been applied. They have 
been considered as characters of sense data, on a par with quality, 
intensity and extensity: and they have been supposed to be 
strictly sexual sense data. Both of these theories may be excluded 
now. Pleasantness and unpleasantness are bodily feeling of a gen- 
eral rather than a localized nature, and the discussion of their 
nature and laws will be taken up in a later chapter. 

Without doubt there are a great number of bodily feelings for 
which we have no names, and concerning whose conditions we 
know little. Observation on them is exceedingly difficult on ac- 
count of our lack of means of control. Some of these vague feel- 
ings, which enter into the more definite emotional complexes, will 
be discussed later. 



CHAPTER V 
SOME DETAILS CONCERNING SENSORY CHARACTERS 

§1. The relativity of sense data. 

In the preceding chapters, the fact has been brought ont that 
the intensity of sense data is not a fixed or absolute quantity, but 
is relative to the perceiving mechanism. The brightness of a light, 
for example, depends upon the adaptation of the eye ; and the same 
light may be quite different in intensity for two different observ- 
ers. This relativity applies not only to intensity, but also to the 
other quantitative characters. The pitch (extensity) of a tone, 
and the size of a retinal or dermal impression are determined in 
part by the physiological condition of the receptors, and their 
anatomical peculiarities. Congestion of the inner ear may raise 
the pitch of notes, and the extensity of a colored area varies in 
different parts of the retina. Duration, and position in time and 
space, are similarly conditional. 

Quality, on the other hand, is not relative. Relativity always 
implies more or less of; and there is no variation of more or less 
in respect to quality. When we speak of more or less of a cer- 
tain quality, we really mean more or less in intensity, extensity 
or duration, of a sense datum of the specified quality. 

For example: a reddish purple color is said to have more red, 
and less blue, than a bluish purple. This means simply that the 
red color is more intense in the first combination and the blue less 
intense (proportionately) in the first combination than in the sec- 
ond. One pure red cannot be either more red or less red than 
another pure red. The differences in color associated with a given 
stimulus, according to the adaptation of the eye, are due solely 
to differences in the proportionate intensities of the component 
primary colors. - 

The stimuli of the sense data, however, are conceived as abso- 
lute, in spite of the quantitative variations in the sense data them- 
selves. Regardless of the brightness of the light as seen by dif- 

112 



SOME DETAILS CONCERNING SENSORY CHARACTERS 113 

ferent observers at a given moment, there is assumed to be only 
one value of the stimulus intensity. This peculiarity of relation 
of sense datum to stimulus has led to the unnecessary and confus- 
ing hypothesis that in every such case the observer is aware of 
an object (" sensation") which is his exclusive property: an abso- 
lutely distinct object for each observer. In reality, the situation 
is much simpler, and much more in accordance with the naive 
view of the man unsophisticated in philosophy. In such cases as 
those to which we refer, the different observers may really see 
the same object; but they see it with different quantitative char- 
acters, since these characters are determined by the perceiving 
organs as well as by the stimulus. Psychology does not drive us 
to abandon the belief in a real perceptible world, however much 
we may vary quantitatively in our perceptions of it, and in spite 
of the fact that some of us may be incapable of perceiving certain 
features of it at all. 58 

§2. Stimulus thresholds. 

Sentienda must satisfy certain conditions in regard to their 
primary characters in order to be perceptible under given condi- 
tions of the organism. These conditions, conventionally called 
stimulus thresholds, are measurable, in terms of the stimuli. The 
term "threshold" is drawn from an old analogy of consciousness 
to a room, into which contents are supposed to enter: but the 
metaphor is mixed by the further convention of speaking of im- 
perceptible and perceptible contents, not as "without" and 
"within" the threshold, but as "below" and "above" respec- 
tively. This mode of speaking arises from our common habit of 
schematizing increasing magnitudes on a line extending upwards 
from zero. In theory there are qualitative, intensive, extensive, 
and protensive stimulus thresholds. These we may refer to as 
the Q.S.T., I.S.T., E.S.T., and P.S.T. respectively. * At present, 
not all of these are measurable for all senses. 

The I.S.T. is the condition of sufficient intensity which a sen- 
tiendum must satisfy in order to be perceptible. A light, for ex- 



5S We cannot deny the possibility of there being qualities which no human being is 
capable of perceiving. There may be qualities corresponding to the infra red and 
ultra violet rays, for example. But Ave cannot affirm their existence. With the exist- 
ence of purely hypothetical entities, neither science nor common sense has any concern. 



114 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

ample, must have a certain minimal intensity in order that it may 
be perceived. Between zero and a certain maximal intensity 
(which we will call IJ, the light is imperceptible: above a cer- 
tain minimal intensity (L) it is perceptible. The interval* from 
li to L is the I.S.T. for light, under the given conditions of obser- 
vation. The measure of the I.S.T. which is actually obtained in 
a series of measurements will, of course, depend upon the magni- 
tude of the unit of measurements, and upon the criteria of per- 
ceptibility and imperceptibility adopted. But in any case, there 
will be an interval between I x and L, and this interval, which is 
the approximate I.S.T., will always include the actual I.S.T., if 
the measurements are reliable. 

For convenience in certain practical applications of threshold 
measurements, the threshold is represented by a single number: 
and the number employed for this purpose is usually the mean of 
the two numbers which represent the approximate threshold, and 
is called the threshold value. Thus, if I x is 24, in the scale of 
measurements adopted; and L is 29, the I.S.T. value is 26.5. This 
value represents the center of the zone within which the senti- 
endum is neither perceptible nor imperceptible : the center of the 
threshold. 

The E.S.T. is the condition of sufficient extensity, and is, of 
course, in anatomical terms the stimulation of at least one recep- 
tor. This threshold is not determinable in terms of the stimulus, 
for the senses generally. On the skin, for example, a stimulus 
will excite at least one receptor, however small the stimulus may 
be areally, if it is sufficiently intense, and if there is actually a 
receptor termination at the point of application of the stimulus. 
In the case of audition, however, on account of the mechanical 
details of stimulation, the E.S.T. is determinable in terms of wave 
length of the stimulus, and is commonly called the upper pitch 
threshold. 

The Q.S.T. is not strictly the condition of quality which a sen- 
tienda must satisfy ; but is rather the condition under which a 
quality may exist: measured, like all thresholds, in terms of the 
stimulus. In the case of light, for example, wave lengths greater 
than a certain magnitude, have no color corresponding to them: 



SOME DETAILS CONCERNING SENSORY CHARACTERS 115 

they are not stimuli of vision at all. Moreover, wave lengths less 
than a certain minimum have no color corresponding. There are 
then, for vision, two Q.S.T.'s, or "wave length thresholds:" and 
the corresponding two threshold values are the "limits of the visi- 
ble spectrum." The lower pitch limit for tones, and the molecular 
weight limit for odors, are also Q.S.T's. 

The P.S.T. can be determined only for specified intensities of 
stimulus. For light of a given intensity and area, for example, 
we may determine the minimal time of stimulation which causes 
perception, and the maximal time which does not. But for higher 
intensities the threshold value becomes lower, and any duration, 
however brief, will produce perception, if the intensity is suffi- 
ciently great. 

§3. Physiological conditions of intensity and quality. 

The intensity of any sentiendum depends, physiologically, upon 
the energy of response of the receptors, and consequent energy 
of the "nerve current" transmitted from them to the central 
nervous system (brain and spinal cord) for reflection outward to 
the effectors. The nature of the energy-variations in nerve cells 
are at present conjectural, but it is certain that these variations 
occur. 59 

The quality of a real sense datum cannot be conceived as de- 
pendent upon physiological processes at all, but the perception of 
all qualities does depend upon reaction, and the perception of any 
given quality depends upon the initiation of the reaction in a 
specific sort of receptor. Color, for example, cannot be perceived 
except through reaction initiated by retinal cone-cells. 

From this dependence of perception upon receptors, it follows 
that whenever the appropriate receptor process is set up, the cor- 
responding quality is perceived, tvhether there is any sense datum 
"really" present or not. Sense data perceived in this way are 
called "subjective" or hallucinatory. From this point of view, 

59 If the "all or none" law is finally demonstrated for nerve cells, that is, if it is 
?hown that any nerve cell can function ("discharge") at any given moment with its 
fullest capacity only, i. e., a maximal discharge; then the variations in energy must be 
conceived as variations in the number' of such discharges per unit of time (e. g., per 
second.) Conclusions on this point must be held in abeyance for the present. 



116 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

inadequate stimuli are the mathematical correspondents of halluci- 
natory sense data. 60 

Idio-retinal light, for example, and the "phosphenes" obtained 
by pressing on the eye ball, or moving the eyes sharply to the side 
(in darkness) ; and the " subjective noises" which occur in the ear 
(not the roaring of the blood stream, but the fine "clicks" and 
screeches which occur in pathological conditions), are sense data, 
with all the fundamental characters; (they are not "real," how- 
ever, in the sense of being external to the organism). These and 
similar sense data are commonly called "subjective sensations," 
which perhaps may be considered properly as organic. 

Hallucination, or experience due to inadequate stimulation of 
receptors, is a process which is intermediate between true percep- 
tion and imagination, and the contents of hallucinatory perception 
are in their nature akin to sensory thought-contents, which are con- 
ventionally called "images." The analysis of thought-reaction, 
which is presented in a later chapter, throws further light upon the 
problem of hallucination. 

The fact that there are hallucinatory sense data has been a 
source of perplexity to the philosophers for five hundred years, and 
had led to the hypothesis that all sense data are unreal in a strict 
sense, and are determined solely by physiological processes. This 
theory, known as epistemological dualism, was introduced by Male- 
branche, and holds that real objects have no quality, and that 
sensory qualities exist only when perceived, and then only ' c in the 
mind" of the perceiver. This view was constructed to meet the 
difficulty of "unreal sense data" above mentioned, and has been 
accepted partially by so-called "common sense," or popular phil- 
osophy, being held there in unresolved contradiction with the view 
that somehow perceived objects are really external objects. The 
term sensation, where used for content, rather than awareness, 
commonly implies this metaphysical theory of dualism. The very 
confusion between content and awareness involved in the term 
"sensation" is the result of the supposition, inherent in dualism, 



coWe say hallucinatory and not imaginary, for, as we shall show later, imagined 
sense data are in many cases ' ' really ' ' existent. Imaginary is not to be contrasted 
with real in psychology, but only with perceived. "Real" is here used in the popular 
significance in which we employ it when we say "I saw such-and-such an object, but 
there was no such object really there." 



SOME DETAILS CONCERNING SENSORY CHARACTERS 117 

that the existence of the sense datum depends npon the perception 
of it. 

The dualistic theory was apparently justified by the principle 
of parsimony, but as we pointed out earlier, this principle alone 
cannot settle the truth of hypotheses. The dualistic theory does 
not resolve satisfactorily the difficulties it was constructed to meet, 
and raises far graver ones. For the present, the more empirical 
view taken in this text is the most satisfactory one available. 

§4. Temporal and spatial characters. 

Duration and position in time are characters which are bound 
up so closely with relational factors that their analysis is exceed- 
ingly difficult, and little has been done with them. Much more at- 
tention has been paid to the spatial characters; extensity and posi- 
tion in space. 

Extensity depends, physiologically, upon the number of recep- 
tors stimulated. This is obvious in the case of vision, audition, and 
the cutaneous senses; but it is not so obvious for the visceral sense, 
where the connections between receptors and central nervous sys- 
tem are of a peculiar sort. The chief difference in the latter case, 
however, is that the extensities of visceral data are in many cases 
relatively large in comparison with the stimuli. The apparent 
extent of a light or pressure area varies according to the partic- 
ular part of the retina or skin affected. A flat disc applied to the 
skin of the palm of the hand is experienced as being larger than 
when applied to the arm. If the disc is pressed down heavily, the 
apparent extensity increases, on account of the larger skin area 
actually affected, and the additional protopathic and muscular 
feelings. 

Area of stimulus affects intensity as well as extensity, because 
of the phenomenon known as irradiation: i. e., the tendency of the 
excitation of one area to affect adjacent areas, thus apparently les- 
sening the stimulation of the original area. On the retina, an in- 
crease in the area stimulated increases the brightness perceptibly, 
if the intensity of the stimulus is kept constant and the areas stim- 
ulated are very small. Beyond the size of a few millimeters, at a 
meter's distance from the eye, the effect of further areal increase 
is negligible. This effect is due in part to dispersion of light in 



118 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

the lens system of the eye, but is in part an actual irradiation 
effect. 

Increasing the area of a small thermal stimulation of the skin 
may increase in two ways the intensity of the warmth or cold ex- 
perienced: by lessening the irradiation, and by including more 
sensitive areas in the stimulated extent. 61 

The lessening of irradiation by stimulating larger areas is due 
to the fact that irradiation affects principally the edges of the 
stimulated area. The intensity of a sentiendum of small area is 
not increased by adding similar stimulation of other areas, non- 
contiguous to the first area, but may be lessened through con- 
trast. 

Retinal irradiation may be demonstrated by comparing the ap- 
parent sizes of a black disc or square on a white ground with a 
white disc or square of equal area on a black ground. The white 
figure will seem to be larger. A field of white discs closely and 
regularly spaced on a black ground, when placed at a proper dis- 
tance from the eye, shows the irradiation effect in the hexagonal 
appearance of the discs. The striking effect obtained by holding 
the edge of a ruler between the eye and a strongly illuminated 
surface of diameter less than the length of the ruler is due only in 
part to irradiation, diffraction of the light rays by the edge being 
an important factor. 

Spatial position as a character of sense data is called local sign. 
Light of the same local sign may have any one of an indefinitely 
large number of positions at different times in external space ; and 
conversely, a visual datum of a given space-position may have 
any of the local signs at different times. The relation between 
local sign and the external position depends upon the relation of 
the external space position to the position of the eye in the socket, 
and to the position of the head. If, for example, the eye "follows" 
an object moving in space, either by rotation of the eye in the 
socket or rotation of the head, the local sign of the object may 
be maintained unchanged. The relation of dermal local signs to 
external space is equally complicated. 



eiBarnhart & Bentley, Am. Jour. Psychol., Vol. 22, pp. 325-332. 



SOME DETAILS CONCERNING SENSORY CHARACTERS 119 

In the auditory data, we have local sign, as well as extensity, 
in its "pure" state, unorganized into indications of external space. 
Although pitch is pure extensity, and pitches may be compared 
directly as such, the local sign of the receptors on which (at the 
variable end of the series) a note of given pitch ends, may assist 
in the identification of the pitch in perception, and in the discrim- 
ination of pitches so close together that as pure extensities they 
are indistinguishable. The difference between the trained or musi- 
cal ear, and the untrained or unmusical ear, in regard to pitch dis- 
crimination and absolute pitch, can be explained on no other basis 
than the reliance on local sign by the individual with the first 
type of audition. This conclusion is in agreement with the fact 
that in vision, discrimination of local sign is far finer than discrim- 
ination of extensities, as is apparently also the case in touch. 
Whereas some "unusual" ears may be trained to a high degree 
of pitch discrimination, others remain "dull" even with maximal 
hearing. In these defective cases, it seems probable that through 
mechanical defects in the auditory apparatus, the tones do not 
terminate sharply at definite points in the series of hair-cells (re- 
ceptors), but taper off diffusely. 

§5. Movement. 

Movement involves time and space, and it is through the com- 
bination of changes in local sign and in the temporal position char- 
acter that we perceive the actual movements of objects in space. 
Since, however, movements of the sense organ, as of the head or 
eyes, or of the hand over an object, can produce the same combina- 
tions of positional character as the movement of an object with 
the sense organ at rest, it is evident that the muscular changes 
(in eye-muscles, neck-muscles, and arm-muscles) are the ultimate 
factors in the perception of movement. Movement, like space and 
time, is a complex affair, and its perception is also complex. 

A moving stimulus, either on the retina or on the skin, produces 
an especially intense series of stimuli, and hence causes perceptual 
reactions of an especially definite and vigorous sort. This ac- 
counts for the fact that moving objects, tactual or visual, will be 
perceived under circumstances where fixed objects of the same 



120 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

stimulus-intensity will not be perceived, either because of their 
low stimulus-intensity, the low efficiency of their receptors (as on 
the peripheral retina), or "distraction'' from other sorts of stimu- 
lation. 62 



62Auditory movement, where the transition from one pitch to another is continuous 
and not discrete — the slurring of notes — has important perceptual effects which merit 
investigation. 



CHAPTER VI 
SOME SIMPLE RELATIONS OF SENSE DATA 

§1. Relations as objects of consciousness. 

Relations can be perceived and thought about, just as sentienda 
may be perceived and thought about. The actual experienced 
world consists of sentienda related to each other in intricate ways, 
and it contains nothing else. This is true, at least, of the world 
exclusive of our experienced bodies: there are no experiencible 
things other than sentienda and relations, unless the feelings which 
are peculiar to our own organisms are to be classed as something 
other than sentienda. If there are objective realities in the outside 
world, besides sentienda and relations, these things are not experi- 
enced, and are not "given" in experience, and hence cannot be 
discussed rationally. 

It is probably true that we can seldom, if ever, be conscious 
of sentienda without relations, or of relations without sentienda 
related by them. Yet it is possible to be conscious of two sen- 
tienda between which there is a specific relation, without being 
conscious of the relation between them: a relation of difference, 
for example, as in the case of two sounds differing in pitch. In 
some cases this failure is merely an accident of perception: a 
chance direction of attention away from the relation at the moment. 
Thus, two tones, differing considerably in pitch, may be heard, but 
the difference may not be observed, although it is of sufficient mag- 
nitude to be perceived readily at other times. 

In other cases, relations may be imperceptible because the in- 
dividual has not yet learned to perceive them. Thus, pitch differ- 
ences which are imperceptible to the unpracticed ear, become 
readily perceptible after sufficient practice in pitch discrimina- 
tion. 63 In still other cases, relations which actually exist between 

G3An individual who is at the first trial unable to distinguish between tones of 256 and 
262 v. s., may, after some days' practice, succeed in distinguishing between 256 and 
257 v. s. 

121 



99 



ELEMENTS OE SCIENTIFIC PSYCHOLOGY 



perceptible sentienda never can be perceived in spite of maximal 
practice and all other possible favoring conditions. For example: 
if three tones are so chosen that the second is just perceptibly 
higher in pitch than the first, and the third is just perceptibly 
higher than the second, a tone may be inserted midway in pitch 
between the first and second, and another midway between the 
second and third. We now have a series of five tones, in which 
the difference between the first and second is imperceptible, and 
the difference between the second and third, third and fourth, 
fourth and fifth are likewise imperceptible. And yet these pitch 
differences actually exist, as is proved by the fact that the third 
is perceptibly different from the first and from the fifth, and the 
second is perceptibly different from the fourth. 64 Obviously, rela- 
tions are objective facts whose reality does not depend on their 
being perceived. 

The analysis of relations is a seriously neglected topic and our 
scientific knowledge of relations is fragmentary. We are not able, 
therefore, to classify them with either certainty or completeness, 
nor can we discriminate the simple or elementary relations from 
the complex. In neither of these directions has much progress been 
made, and our knowledge of relations remains in very much the 
same unsatisfactory condition as our knowledge of odors. At the 
most, we can but list certain relations which are of the first rank 
in scientific interest, and which perhaps are simple. Among these 
are: difference, resemblance, identity, magnitude, intermediacy 
(betweenness), concomitance, causality, inclusion, and certain 
time-relations and space-relations. 

Time and space, as perceived, involve many relations in addi- 
tion to the peculiar constituent ones. Magnitude and betweenness, 
for example, are both involved in time and space. A certain stretch 
of time or space may be greater or less than another. The second 



6*If we represent the five pitches by p 1? p 2 , p 3 , p 4 , p 5 , we can show that p 2 must be 
different from p a ; otherwise it would be perceptibly different from p 3 ; and that p 2 
must be different from. p 3 , otherwise it would be perceptibly different from p 1# And 
so also we can show that p 4 is really different from p 3 and p 5 , although the differences 
are imperceptible. These facts apply to the sounds themselves (" sensations " f in the 
confused terminology of the past), and are among the inescapable reasons why we 
must distinguish between sentienda ("sensations") and the awareness, or conscious- 
ness, of the sentienda. 



SOME SIMPLE RELATIONS OF SENSE DATA 123 

moment of a time series, or the second position on a line, lies be- 
tween the first and third. But magnitude and intermediacy are 
not peculiar to space and time: there are magnitudes and inter- 
mediacies which are not spatial or temporal. 65 On the other hand, 
there are certain relations which occur only in space or in time. 
The essential factor in time is the peculiar time-relation which we 
call succession. And this is one of the most important of all rela- 
tions, for every concrete thing either succeeds or follows or is 
simultaneous with, everything else in the universe. 

Simple relations, and relations which appear simple, are like 
simple sentienda in that they cannot be described. We can point 
out what we mean by one of the names, only by indicating a situa- 
tion in which the relation is involved, and other situations in which 
it is not involved. The indescribability of any specific relation is 
a reason for tentatively supposing it to be simple rather than com- 
plex. 

Because sentienda and relations are not practically isolable 
from each other, it is necessary to treat certain aspects of relation 
in connection with the characters of sentienda. But the charac- 
ters of sentienda are to be distinguished from the relations which 
subsist around them. This distinction is especially important, and 
especially difficult, in the case of extensity and protensity. Exten- 
sity is essential for space relations, but it is not the space relation 
itself. Sentienda could not be in time if they had no protensity, 
yet protensity is not succession. 

Relations exist primarily between sentienda; but relations 
themselves may be related in almost endless complications. Let 
us suppose two sounds, between which there is a certain differ- 
ence in intensity, which we will call di, and another pair of sounds 
between which there is another intensity difference, cl 2 . Now di 
and d 2 may be equal, that is to say, identical in so far as we con- 
sider the relations abstractly: or, they may differ, with a differ- 
ence d', (a difference of the second order). We may suppose now 
two other pairs of sounds, with intensity differences d 3 and cl 4 , 

eslntensity, for example, is magnitude. A patch of light may be more or less bright 
(intense) regardless of its spatial and temporal relations. And there are also inter- 
mediacies of intensity: one light may be between two others in brightness, regard- 
less of the time and space relations of the lights. So there may be intermediacies 
cf qualitative complexes: orange is between red and yellow in hue. 



124 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

with a difference d" between d 3 and d 4 . Once more, d' and d" may 
have a difference of still higher order, and so on. Moreover, a 
pair of sonnds may differ not only in intensity, di, but also in 
pitch, dx: and there is a definite difference between d ± and dx. 

The complications of relations are endless, bnt all relations rest 
ultimately in sentienda. Even the complex relations of mathe- 
matics and morals, which are treated abstractly, depend for their 
reality on ultimately related sense data. 

§2. Identity and difference of sense data. 

The identity and difference of sentienda with respect to their 
characters are especially important. The perception of difference 
in quality (differences in color, in odor, etc.) ; of intensity (loud- 
ness, brightness, etc.) : of extensity: of duration and of position are 
involved in almost all the practical reactions of life. Difference 
may be perceived with great clearness, if the differences are suf- 
ficiently great; but identity can never be distinguished from dif- 
ferences which are imperceptible. Thus, if two lights differ largely 
in intensity, the difference may be unmistakable: but if no dif- 
ference is perceptible, one cannot be sure, from immediate obser- 
vation, that the two are actually identical, rather than differing 
by an imperceptible amount. As we have seen in the preceding 
section, it is possible to show that certain data which are appar- 
ently identical in one of their characters, are really not identical. 

The measurement and comparison of differences is an impor- 
tant part of experimental procedure in psychology. Such meas- 
urements deal with immediate differences in respect to sensory 
character, and with identities and differences of differences, but 
not with differences higher than the second order. 

§3. Threshold differences of sense data. 

Since differences may be so small as to be imperceptible, it is 
obvious that there must be difference thresholds, just as there are 
stimulus thresholds. If we compare, for example, a tone of stand- 
ard pitch, P, with a series of tones, p 1? p 2 , p 3 , etc., varying by small 
gradations above and below P, we shall establish four important 
values of p. These are: p A , the least value of p which is percep- 
tibly greater than P; p a , the greatest value of p which is not per- 
ceptibly greater than P; p B , the greatest value of p which is per- 



SOME SIMPLE RELATIONS OF SENSE DATA 125 

ceptibly less than P; and p b , the least value of p which is not 
perceptibly less than P. 66 Two threshold values are thus deter- 
mined: one, Pa, by a point intermediate between p A and p a ; the 
other P/?, by a point intermediate between p B and pu, each thresh- 
old point being the mean of two differences between P and p, 
and representing a difference which is neither perceptible nor im- 
perceptible. These two threshold values are not necessarily equal. 
The difference threshold (D.T.) is properly represented, not 
by the absolute difference between P and p, but by the ratio of 
this difference to P, which may be expressed as a ratio or per- 
centage. For example: if P is 100 vibrations per second, and the 
four vibrations rates of p are 96, 98, 101, and 103, the threshold 
points in the scale of measurement are 97 and 102. The thresh- 
olds are not properly expressed as 3 and 2 (100-97 and 102-100) ; 
but as 3/100 and 2/100. This method of expression is important 
for the understanding of Weber's Law. 

§4. The intensity difference threshold and Weber's law. 

A significant constancy of the intensity difference threshold 
has been observed, and is generally designated as Weber's law. 
Unfortunately, the physiological texts, and some psychological 
texts, confuse this principle with a mathematical interpretation 
thereof, properly called Fechner's laiv, or Fechner's formula. 67 It 
is important that the student should distinguish clearly between 
these two. 

Weber's law can be stated briefly as follows: The intensity 
difference threshold expressed as a ratio (or percentage), is ap- 
proximately constant for changes in intensity of stimulation alone, 
throughout a certain limited range of intensities. 

For example: if the threshold difference for a gray of 100 
units brightness is 1 unit, the threshold difference for a gray of 
500 units brightness will be 5 units: the threshold ratio in each 
case being 1:100. And this same threshold will hold for values 

66The values p A and p R are sometimes taken as threshold values, instead of Pa and 
P/3. But p A -P and P p/3 are just perceptible differences (j. p. d.) : commonly termed 
just noticeable differences (j. n. d.), £ixicl obviously are slightly greater than the true 
threshold-differences. 

67Weber's law was discovered and formulated by G. T. Fechner from a study of 
tactual intensity difference thresholds obtained and reported by E. H. Weber, and 
given Weber's name by the discoverer. 



126 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

of the stimuli intermediate between 100 and 500, and for a cer- 
tain extent of the range above and below these values. 

The limitations of Weber's law are important. In the first 
place, it applies to intensity differences only: this fact needs 
especial emphasis, since assumptions that it should apply to other 
characters have spoiled many discussions of sensory psychology. 
In the investigations of quality and extensity differences, no prin- 
ciple analogous to Weber's law is found. 68 In both of these fields, 
the difference thresholds are more nearly constant when expressed, 
not as ratios, but as absolute differences. For example : in the 
case of the pitch-difference threshold, for wide variations of P, the 
threshold difference P-p is approximately constant, the ratio of 
this threshold difference to P, therefore, not being constant. In 
the case of tactual and visual extensities, the difference threshold 
varies with the spatial and temporal details of comparison, but 
follows the rule for pitch difference if the areas compared are 
superposed on the same sense area, either simultaneously or in 
immediate succession. Qualitative difference thresholds, and 
thresholds of duration difference, follow no such simple laws. 

The second important limitation acknowledged by Weber's law 
is that of range. In any case, constancy of the threshold holds 
for a certain range of stimulation intensities, and fails both above 
and below this, the threshold usually becoming greater for both 
the too high and the too low intensities. 

In the third place, the law holds for the same sort of stimula- 
tion only. The threshold value for one sense is not the same as 
for another: and within the same sense, the thresholds may differ 
for different stimuli. Thus, the difference threshold determined 
for a certain range of red light intensities cannot be expected to 
hold for any range of blue light intensities. 

Finally, the physiological and psychological condition of the 
individual must be approximately constant. Thresholds deter- 
mined for one person will not, in general, hold for another; and 
thresholds determined in states of fatigue, or inattention, or dis- 



tfsCertain observations do seem to show, however, that the D. T. for the size of detail 
in pattern-vision follows a law analogous to Weber's, if the absolute size of the 
stimulus details is well above the stimulus threshold. See Johnson, H. M., in the 
Journal of Animal Behavior, 1916, Vol. VI, pp. 169-221. 



SOME SIMPLE DELATIONS OF SENSE DATA 127 

ease, will not necessarily agree with those determined for the same 
subject in vigorous health, and with proper attention. 

Fechner's formula was developed from Weber's law by mak- 
ing the following assumption : that threshold differences in inten- 
sity of sense data, under the conditions for which Weber's law 
holds, are all arithmetically equal. For instance, it is assumed 
that the difference in brightness between the light of 100 units 
brightness and the light of 101 units is exactly the same in magni- 
tude as the difference between the light of 500 and the light of 
505, if these are threshold differences. Yet the measures of these 
differences are not arithmetically equal, but are geometrically 
equal; that is, they are equal ratios. 

By a simple mathematical operation, this assumption leads to 
a formula in which the relation of any actual intensity of a sense 
datum to the measured intensity of the stimulus is given. The 
formula is: 

S - C log R 

where S is the intensity of the sense datum ("sensation"), and 
R is the intensity of the stimulus, ("Reiz") K and C being con- 
stants which are valid for the particular mode and conditions of 
measurement. 

The assumption upon which Fechner's formula is based is ob- 
jectionable for many reasons. In the first place, it is quite arbi- 
trary, and has no foundation except its necessity for the develop- 
ment of the formula. In the second place, it is contradicted ap- 
parently by the actual facts in the case of light intensities, since 
Weber's law holds for light intensities when measured by the 
visual comparison procedure; in which case that which is com- 
pared are not the true physical stimuli, but the perceptible bright- 
nesses themselves. 69 In other words, it is clear that in the case of 
light intensities, the absolute value of the threshold difference 
does increase as the standard brightness increases. 



69The scales of measurements in which light intensities are measured are psychological 
rather than physical, since they are derived by direct observation of brightnesses, the 
measurements depending upon threshold determinations. The ' ' stimulus ' ' measure- 
ments of light, in fact are standardized with reference to intensity difference thresh- 
old measurements. That Weber's law should hold for light intensities is, therefore, 
a striking refutation of Fechner's fundamental assumption. 



128 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

Finally, experimental work on an intensity deduction from 
Fechner's formula throws additional doubt upon it. If the assump- 
tion upon which the formula is based were valid, then (as can be 
shown mathematically), where two clearly perceptible differ- 
ences in intensity of a certain sense datum are perceived as equal, 
the stimulus differences should be in equal ratio. For example : the 
difference between intensities 100 and 150 should appear equal to 
that between 150 and 225. In experimental tests, this expecta- 
tion is sometimes realized, but sometimes it is not. In some 
cases, for example, where observers are required to divide the 
difference between two intensities by adjusting a third in- 
tensity to be midway between the two, the geometric mean 
is frequently chosen, but often the arithmetic is chosen. There 
is no escaping the conclusion that "equality" means sometimes 
equality of absolute measure, and at other times, or to other per- 
sons, relative equality. 

Weber's law is of theoretical interest, but its practical aspects 
are perhaps discouraging. Intensity difference thresholds actually 
vary enormously in all senses, in accordance with the method of 
presentation and comparison of the intensities. This, of course, 
does not invalidate Weber's law, since it specifically applies only 
to conditions where the methods are uniform. But it has pre- 
vented the determination of any standard, either of range or of 
threshold constants for the various senses. 

In the case of pressure applied to the skin, if two intensities 
are applied to the same area, briefly, and in rapid succession, the 
D. T. may be as low as 1 : 100, with 50 to 100 grams standard. But 
if applied for longer periods, or with several seconds between the 
intensities, or if the two are applied on different skin areas, the 
ratio may run to 1:5 or even more. It seems probable that in all 
the senses, under optimal conditions of stimulation, the D. T. ratio 
for a certain range of intensities may be as low as 1:100, or even 
lower, for normal healthy individuals, with sufficient practice in 
difference discrimination. With defective sense organs, feeble- 
mindedness, ill health, or non-optimal conditions of test, the ratio 
increases. 



SOME SIMPLE RELATIONS OF SENSE DATA 129 

§5. Intermediacy or betweenness. 

Intermediacy is one of the most important of the relations of 
sense data for onr analysis of these data, and it is through use 
of this relation that we are able to schematize the elementary data 
as we have done in the preceding chapters. A sense datum may 
be intermediate between others in many different ways ; but inter- 
mediacies in respect to the characters earlier listed are most im- 
portant for our purposes. These intermediacies, except for space 
and quality, are all linear, and susceptible of gradations. Inten- 
sities, for example, may be schematized as a line; and since 
for a pure linear series there is no question of direction in any 
other dimensions, they may be schematized as straight lines. In- 
tensities constitute a potentially continuous gradation, since there 
is a possible intermediate degree between any two intensities, 
whether perceptible as intermediate or not. This continuous 
gradation is simple in the case of all quantitative relational senses, 
but with respect to qualitative gradations there is the following 
peculiar situation which we have already noted. 

In any quantitative series, there are two extremes, and any 
other member of the series is intermediate between the two. In 
qualitative series, such as those of taste and vision, there are no 
extremes, and certain terms in the series are non-intermediate to 
certain other terms, although they are intermediate to still others. 
In the color series, for example, R is not intermediate in quality 
to C and B. There is no respect except the purely spatial one of 
the spectrum in which any of these three is behveen the other 
two. Yet there is a gradation of intermediacy of many hues be- 
tween pairs of these — such as the purples, between R and B; the 
orange reds, oranges and yellows, between R and C ; and the greens 
and blue-greens between C and B. This peculiarity of the color 
series is responsible for our concluding that the series is based 
upon three fundamentals in the color series, and is intelligible as 
soon as we conceive of them as fixed elementary colors, and the 
gradations between them as mixtures. 

The existence of critical points in a qualitative series is of the 
highest importance for sensory analysis. Through this we were 
enabled to decide that the pitch series is non-qualitative; and it 



130 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

furnishes an additional support for the "three-color theory" of 
vision, since four mutually non-intermediate colors cannot be 
found. Furthermore, it is through the use of critical points that 
we can eventually determine the exact primary colors. The R or 
the B may not be in the spectrum at all: this point has been ad- 
mitted by almost all theorists. The primary red may be a hue 
more purplish than the extreme red of the spectrum: or the B 
may be actually more violet than the extreme short wave end of 
the visible spectrum. But the C color must be in the spectrum, 
and its determination is the determination of a critical point 
within the spectrum; a determination which is quite possible, al- 
though as yet it has been made but roughly. 



CHAPTER VII 
SOME SENSORY MEASUREMENTS 

§1. Measurements and tests. 

It is neither feasible nor desirable to introduce here a detailed 
account of the methods and instruments required for accurate 
measurement of sensory capacity. Such an account must neces- 
sarily be both technical and voluminous, and is given properly in 
a laboratory course : the technique of accurate measurement can 
be acquired only by a laborious process under competent super- 
vision. There are many pitfalls for the unwary, and an exten- 
sive range of cautions must be observed; so that it is impossible 
for the untrained worker to obtain reliable results, except for 
clinical purposes where comparatively rough measurements will 
suffice. It is possible, for example, to diagnose a grave defect of 
vision or of audition by the rough methods commonly employed 
in medical practice; but the lesser defects, even some of those 
which may have serious practical consequences, and the differ- 
ences in sensitivity of "normal" individuals, can be measured only 
by the refined methods of the psychological laboratory. 

The methods and technique of accurate measurement include 
not only a precise instrumental technique, and exact methods of 
presenting stimuli with proper gradations and order, but include 
also the proper time arrangement; the use of carefully planned 
warning signals; and various detailed provisions to secure uni- 
formity of attention, lack of bias, and absence of emotional dis- 
turbance on the part of the reactor. 

In certain cases, it is important and possible to make deter- 
minations in which small units of measurement are not demanded, 
and in which the reactor is not required to determine just per- 
ceptible and just imperceptible values. Such determinations are 
called tests; and although in each case certain details of technique 

131 



132 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

are indispensable, this technique is neither as detailed nor as dif- 
ficult of acquisition as the technique of exact measurement. 70 

The measurements described below are applicable directly to 
the Stimulus Threshold (ST), 71 the Difference Threshold (DT), 
and the Range of Sensitivity (RS), but are capable of extension 
to cover a much wider range of functions, such as the adaptation 
process. 

§2. Olfactory and gustatory measurements. 

The most obvious method of measuring olfactory and gusta- 
tory sensitivity is by means of odorous substances dissolved in 
dry air; and sapid substances dissolved in distilled water. The 
1ST for taste and the 1ST for smell are stated commonly in terms 
of the relative parts of the specific substance to parts of air or 
water by weight, which make the substance just perceptible. This 
measurement is not accurately the 1ST, which is a trifle below 
the "just perceptible" point: the exact 1ST is not deducible from 
measurements in which the just perceptible quantity (JPQ) alone 
is given. 

Theoretically, it should be possible to measure the 1ST (or the 
JPQ) by the method described. Actually, the difficulties are great, 
and for olfaction they are almost insuperable. 

In measuring gustatory sensitivity, one may prepare, for a 
given substance for which the 1ST is desired (e. g., cane sugar), 
a series of solutions of graded concentration, and proceed by pre- 
senting these to the reactor for determination. The series of con- 
centrations must be prepared with reference to the degree of ac- 
curacy required in the measurements: that is, the steps between 
successive degrees of concentration employed must be as small as 
the specified limit of measurement. If it is required that the 1ST 
for sugar shall be determined to the nearest unit per cent, the 
concentration must increase (and decrease) by units per cent. 
The series of solutions employed, in that case, will be concentra- 



™The brief account of measurements and instruments included here is intended 
merely as a set of prepared notes, to which the student may refer and relate the dem- 
onstrations and further details which may be given by the instructor. 

7iThe ST is sometimes designated the EL, from the German "Reiz" (stimulus) and 
the Latin "Limen" (threshold). The DT is sometimes designated the DL. Such 
usage is needlessly ponderous. 



SOME SENSORY MEASUREMENTS 133 

tions of 1%, 2%, 3%, and so on, or of 1%, 2%, 4%, 8%, and so 
on, the geometric series being more suitable than the arithmetic 
for some purposes. If, however, a finer measurement is required, 
the successive concentrations in the series must differ by smaller 
amounts. 72 

The temperature of the solution must be kept constant, and 
the quantity of solution applied, as well as length of time during 
which it is applied, also must be kept constant. Conditions of 
attention and fatigue must be standardized by elaborate precau- 
tions in procedure. 

The solution may be applied in quantities sufficient to bathe 
the entire tongue (i. e., a measured "mouthful" may be taken). 
In this case, the mouth must be washed out each time, with a 
measured quantity of distilled water, during a measured length 
of. time, with standardized position or movement of the tongue 
and mouth. These precautions are required, not only to remove 
any sapid substances already in the mouth, including saliva and 
remnants of preceding stimulus solution, but also to minimize the 
effects of saliva in diluting the stimulus solution. 73 

The secretion of saliva is so irregular that the " mouthful" 
method is less satisfactory than the " local" method, which more- 
over must be employed where it is desired to test local distribu- 
tion of sensitivity. In the local method, a portion of the tongue 
is cleansed with distilled water, dried by a non-sapid absorbent, 
and then the solution "painted" upon the area under investiga- 
tion — perhaps a single papilla — by means of a camel's hair brush. 
By this procedure, dilution effects are minimized, and exact local- 
ization of sensory areas is determined. The results, however, 
are not indicative of the sensitivity obtaining under normal con- 
ditions, which are more nearly represented by the "mouthful" 
method. 



72 The conditions laid down here apply to sensory measurements in general. Various 
attempts have been made to calculate the ST and DT in units smaller than the units 
of measurement, as if one should use a series of solutions differing by steps of 5%, 
and from the result attempt to calculate the ST to the nearest unit per cent. Such 
calculations are of no practical value. 

7 3lt is assumed that the mouth and teeth have first been thoroughly cleaned mechani- 
cally. 



134 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

Olfactory measurements present still greater difficulty. Ap- 
paratus for the introduction into the nostrils of measured quan- 
tities of dry air, at determinate temperature, and containing deter- 
minate percentage of gaseous substance, has been ideally planned; 
but no such apparatus has been made practically available. The 
difficulty of maintaining a specified concentration of the odorous 
substance, avoiding precipitation on the sides of containers, etc., 
is so great that fixed gases only could be employed with accuracy; 
and even so, the apparatus would be so complicated that it would 
be applicable only to highly specialized research. 

As a substitute method, solutions of odorous substances in non- 
odorous media have been employed. Various concentrations of 
butyric acid in water, for example, may be employed in this way, 
the reactor being allowed to "sniff" at broad mouthed bottles, 
which contain standard quantities of the solution at standard tem- 
perature. This solution method is admittedly rough, but it is the 
best practically available. The odorous substances soluble in 
water are limited in number, but it is possible that non-odorous 
solvents for oils and resins may be found. 

The needs and difficulties of olfactory measurement have led 
to the construction of an "olfactometer" by Zwaardemaker, which 
is ingenious but not practically satisfactory. In Zwaardemaker 's 
olfactometer, a glass tube has one end curved for insertion in the 
reactor's nostril; over the straight outer portion of the tube is 
fitted a porous porcelain cylinder, which is to be soaked in a solu- 
tion of an odorous substance. As this cylinder is drawn outward, 
a greater length of its inner surface is exposed to the current of 
air drawn through the tube as the reactor inhales. The solution 
impregnating the porcelain cylinder is assumed to be of a stand- 
ard concentration, and at a standard temperature; the air inhaled 
must be of a standard temperature and humidity, and the inhala- 
tions must be as nearly as possible of standard length and energy; 
and preceded by standardized ventilation of the nasal cavities 
with dry air. This- method meets so many points of difficulty that 
it is practically no better than the simple solution method, and the 
instrument has been useful principally as a laboratory instrument 
for the development of technique. 



SOME SENSORY MEASUREMENTS 135 

§3. Visual measurements. 

Measurements of visual capacity, aside from the function of 
the extrinsic muscles of the eye, which control convergence and 
shifting of the direction of vision, may be classed under two heads : 
measurements of sensitivity, and measurements of acuity. Acuity 
is in general the ability to distinguish space-forms, where these 
are of small magnitude; and specifically, the power to distinguish 
lines and points. Acuity depends both upon what physicists call 
the "resolving power" of the lens system of the eye, and also 
upon the perfection of function of the retina. Assuming that the 
lens system of the eye is "normal," or so corrected by external 
lenses as to give the sharpest possible retinal image, further varia- 
tions in acuity depend upon irradiation and the difference-sensi- 
tivity for brightness of the part of the retina stimulated. If, for 
example, the images of two bright lines, separated by a dark strip, 
fall upon the retina, the stimulated areas will not be sharply de- 
fined, physiologically, but will spread by irradiation into the dark 
strip. The lines will be seen as two, therefore, when the geomet- 
rical images of the bright lines are separated sufficiently, so that 
the center of the strip between them is perceptibly darker than 
the central portions of the two bright lines. 

The optical properties of the lens system of the eye may be 
measured by the methods of physiological optics, and defects in 
the lens system approximately corrected. The typical defects 
clinically recognized and corrected are: (1) hyperopia, or hyper- 
metropia, (2) myopia, and (3) regular astigmatism. In the first 
of these, the refractive power of the lens system is too small for 
the length of the eye: 74 in the second, the refractive power is too 
great for the eye length; and in the third, the refractive power 



74The abnormality usually consists in an unusual length of the eyeball, and not in 
a lens of unusual refractive powers. In the hyperopic (hypermetropic) eye, for 
example, the lens is usually normal, but the eye is so short that a lens of increased 
refractive power is required. 

An ocular defect of a different sort, namely presbyopia, or old-sightedness, due 
to hardening of the crystalline lens, and consequent loss of power to accommodate the 
eye for near vision, is also corrected by convex lenses. But whereas true hyper- 
metropia can be corrected for all distances by a single lens, so that the hypermetropic 
eye, with proper lens, becomes virtually a normal eye; presbyopia can be corrected 
by one lens for a certain range of distance only. Hence, the presbyopic eye may be 
normal for ''far vision" without spectacles: requiring "reading glasses" for short 
range, and sometimes glasses of slightly less curvature for ' ' middle range. ' ' 



136 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

is greater in one meridian than in the meridian at right angles 
to that. Corrections are made therefore for the three cases by 
spectacles with (1) convex lenses, (2) concave lenses, and (3) 
lenses of cylindrical curvature. Since these defects result in 
lowered acnity of vision (although they may not be the sole cause), 
the usual oculist's practice is to determine by a trial-and-error 
method the sort of lens which will approximately correct the de- 
fect and produce the maximal acuity for the eye tested. This 
method, since it relies upon the critical observation of the reactor 
himself, involves in high degree the usual difficulties of psycho- 
logical measurements, and is successful only in the hands of the 
expert who understands the psychological difficulties, except 
where merely rough correction of a gross defect is desired. This 
results in the large percentage of misfits in oculists' prescriptions. 
This method, of course, cannot be used successfully on children, 
and the more careful oculists substitute other, and objective 
methods in examining children's eyes. 

The determination of retinal acuity, when defects in the lens- 
system are assumed to have been corrected, or the determination 
of total acuity, when the lenticular and retinal factors are not dis- 
criminated, is also a psychological matter. For exact measure- 
ment, the minimum visibile 75 is determined. The minimum visibile 
is the smallest separation, measured in angle of vision, between 
two lines, or two points, which can be discriminated as two, in- 
stead of fusing into one. Whereas it might be supposed that the 
minimum visibile is a matter of retinal local sign ; i. e., dependent 
upon the smallest perceptible difference in local sign; this is not 
the case. The minimum visibile is fundamentally a matter of dif- 
ference-sensitivity for brightness, two points being distinguishable 
as two when the area between the images of the two in the retina 
is distinguishably brighter or darker than the two images. 

The minimum visibile may be measured by presenting two black 
lines drawn close together on a white surface, and finding the dis- 
tance of the surface from the eye, at which the two lines are just 
distinct, and the distance at which they fuse into a single line. 
The measurements can be transferred into visual angles, from the 



7oPronounced viz-i-beel ; with accent on last syllable. 



SOME SENSOKY MEASUREMENTS 137 

known distance between the lines, and the distances of the lines 
from the eye. In using this method, however, the lines should 
always be six meters or more from the eye, since nearer positions 
introduce differences in accommodation of the eye for the differ- 
ent distances. Theoretically, the lines could be fixed in distance 
from the eye, and the distance between them varied. On account 
of the difficulty in making the small adjustments necessary, this 
method is not easily employed. A single line, which is doubled 
by use of an Iceland spar prism; or a device such as the Ives visual 
acuity instrument, which produces a field of lines of variable 
width and separation by means of a special optical system, may 
be used. 

The most reliable measurements with sharp white lines varied 
in angular separation on a black ground, gives a measure of acuity 
for "normal" eyes under Y visual angle of separation of the lines. 
With optimal conditions of illumination and observation, this meas- 
ure may be brought to 30", and to 15" for unusually acute eyes; but 
1' is considered as "normal," or satisfactory acuity, indicating 
that both retinal conditions and the refraction of the lens system 
of the eye are sufficiently good for practical vision. 

For rough tests of the refraction of the eye, assuming that the 
retinal conditions are approximately "normal," Snellen's Letters 
are used. These are specially designed, square-formed capital 
letters, arranged in horizontal rows, each row containing letters 
of a single height. It is assumed that a letter of 5' angular height, 
the thickness of the lines of the letter being 1', should be "read" 
correctly by the normal eye. The rows of letters are so made that 
the letters of one row will subtend the standard 5' angle at a dis- 
tance of 3 meters from the eye: the letters of the next row sub- 
tend the 5' angle at a distance of 4 meters, the next at 6 meters, 
and so on, up to 60 meters. A working distance of 6 meters is 
usually adopted as a standard, and the acuity is designated in 
terms of the ratio of the actual reading distance, to the distance 
from which the smallest letters which can be read will subtend 
an angular height of 5' at the eye. For example : if a patient, at 
6 meters distance, can just read the row of letters which subtend 
an angle of 5' at 15 meters by the normal eye, his visual acuity 



138 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

is said to be 6/15 or 2/5 of normal. It is necessary in some cases 
to paralyze temporarily the muscle of accommodation (ciliary 
muscle) by means of atropin, or an atropin derivative, in order 
to measure the acuity in the "resting" condition of the ciliary 
muscle, and this procedure is commonly employed by oculists. 
Optometrists, on the other hand, proceed without atropin. The 
psychological factors of the test are so important that better re- 
sults are frequently obtained by careful technique, without atropin, 
than by careless technique with atropin. Nevertheless, certain 
errors, notably hyperopia, are so concealed by spasm of the ciliary 
muscle that their extent is not disclosed without the use of atropin 
or some other cycloplegic. 76 

A simple visual acuity instrument devised by P. W. Cobb pre- 
sents two white rectangles on a black ground. The white rectangles 
are always equal in width to the black strip separating them, 
whereas the width of the rectangles can be varied from zero to a 
sufficient maximum by continuous gradations. In one labora- 
tory form of the instrument, the maximal width of each of the 
white rectangles is 5 millimeters, and the length is constantly 
maintained at three times the width; so that the total figure pre- 
sented is always a square. The axis of the figure can be rotated 
through 180°, so that the possibility of guessing is minimized. For 
general experimental and test purposes, this instrument has many 
advantages. 

Sensitivity of vision is measured in terms of the light falling 
upon a given area of the retina. The unit of luminous intensity 
is that of the flame of a supposed standard candle, 77 and a surface 
is rated in a rather indirect way by its relation to this standard. 
The unit of Brightness, the "candle per square centimeter" is the 
brightness of a surface such that a square centimeter of the sur- 
face has exactly the illuminating power of a standard candle. 

The unit of illumination must not be confused with the unit 
of brightness. The illumination-unit is the meter-candle; that is: 



76A cycloplegic is a drug which paralyzes the ciliary muscle and so prevents accom- 
modation. A mydriatic -dilates the pupil, either by causing strong contraction of 
the radial muscular fibers of the pupil, or by paralyzing the circular fibers. 

^Actually, the standard of luminous intensity is a certain electric lamp, kept by the 
Bureau of Standards at Washington. This lamp has a certain candle-power (luminous 
intensity) when operated under specified electrical conditions. 



SOME SENSORY MEASUREMENTS 139 

the density of light thrown by a standard candle on a surface at 
a distance of one meter from the candle. The brightness which 
such a surface will have depends upon how much of the light thus 
falling upon it is absorbed, and how much reflected; and also upon 
the character of the surface, whether it is specular (like glass or 
a polished metal), or matt (like paper or chalk). In general, any 
surface will present different brightnesses from different points 
of view. In any case, all measures, both of brightness and illumina- 
tion, are ultimately made by the purely psychological equation of 
brightnesses. The measurement of light by such methods is called 
■photometry. 78 

The sensitivity of the eye varies with adaptation, and is so 
great in darkness adaptation that the technique of measurement 
for the normal eye is very difficult. Bough tests of adaptation 
and of the sensitivity of different regions of the retina are easily 
made in a dark room by illuminating a small surface, such as a 
square of milk glass, set in the front of an illuminated box. If 
the light transmitted through the glass be decreased by dia- 
phragms and diffusing screens, a point in brightness may be found 
such that the light is invisible to one coming into the dark room 
from daylight, but will appear after several minutes. The bright- 
ness may be made so low that fifteen or twenty minutes adapta- 
tion is required to make the light visible. At a certain bright- 
ness the light may be visible to the paracentral retina, so that 
it is seen by looking slightly to one side; and yet be invisible to 
the fovea, and hence it will disappear wmen the gaze is centered 
upon it. Adaptation is not as great in the fovea as in the other 
portions of the retina, but even in the fovea some adaptation 
occurs. 

The difference threshold for brightness is measured by sev- 
eral means. The most direct method consists in obtaining the 
brightness on contiguous parts of the same surface, so as to obtain 
the just perceptible and just imperceptible differences. This is 
the method of direct comparison, a less exact and more rapid form 
of which is the method chiefly used in photometry. 



78 For discussion of units of light measurements, see Cobb, Photometric Considera- 
tions Pertaining to Visual Stimuli. Psychological Review, Vol. 23, pp. 71-88. 



140 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

The difference sensitivity on a small central area of the retina 
has been shown to depend npon the brightness of the surround- 
ing field, being greatest when the surrounding field is approxi- 
mately equal in brightness to the brightness for which the 
threshold is being measured. 79 With decreased brightness in the 
surrounding field, the difference sensitivity for a small central area 
falls off slightly: with increase in the surrounding brightness, 
over that of the central area on which measurements are made, 
the sensitivity falls off very rapidly. For the optimal condition, 
the threshold is about .3 of one per cent, where the standard bright- 
ness is 17 candles per square meters. For the same brightness 
of surrounding area, with changes in the brightnesses compared 
in the small central area, the threshold rises to one per cent at 
1/10 the brightness of the surroundings, and .4 of one per cent at 
the brightness of 10 times the surroundings. Obviously, Weber's 
Law does not hold for brightness differences, unless the surround- 
ing area and the area of discrimination are approximately of equal 
brightness. 

In another method (flicker photometry) the two brightnesses 
are obtained alternately on the same area, at rates of alternation 
so slow that flicker is obtained if the brightnesses are sufficiently 
unequal. After having determined the upper and lower thresh- 
olds for brightness difference, by either the method of direct 
comparison or flicker photometry, the point of brightness equality 
between the two lights used may be assumed to be the point mid- 
way between them. As a matter of fact, in photometry, this point 
is estimated by adjustment. In both flicker photometry and direct 
comparison photometry, the most accurate work is done by means 
of beams of light falling upon " white' ' diffusing surfaces, with 
or without lens systems introduced between surface and source, 
or surface and eye. The physical intensity of one or both beams 
employed may be reduced by several methods: (1) By increasing 
the distance between the source and the surface. The brightness 
of the surface varies inversely as the square of the distance from 
the source, if a point source be used; and with a very small source, 
such as a short length of incandescent filament, the assumption 



79P. W. Cobb, Journal of Experimental Psychology, Vol. I, 1916, pp. 540-566. 



SOME SENSORY MEASUREMENTS 141 

that it is a point gives results which are approximately accurate. 
(2) An absorbing screen, such as "smoked" glass, of known ab- 
sorption power, may be inserted between source and surface, or 
between surface and eye. Such smoked glass, if white light is 
employed, must be "non-selective," i. e., it must absorb all 
visible rays in equal proportion. In the case of colored 
light, including several wave lengths, the screen must have 
equal absorbing ratios for all wave lengths employed. (3) The 
beam may be interrupted by an episkotister : a rotating disc 
with "open" (cut-out) and "closed" sectors of adjustable 
angular width. If such a disc is rotated at a speed higher 
than the critical frequency, the reduction in the energy of 
the beam, and consequently of the brightness of the sur- 
face, is proportionate to the ratio of closed sectors to the total 
disc. This is in accordance with the Talbot-Plateau Law, which 
may be stated as follows: If a surface is illuminated by an inter- 
mittent beam of light, the rate of intermittence being above the 
critical frequency for the beam, the brightness of the surface will 
vary directly as the duration of illumination divided by the total 
time. For example: if the open sectors in the disc total 120°, and 
the closed sectors therefore total 240°, the reduction in brightness, 
provided the rate of interruption is greater than the critical fre- 
quency, is 2/3; and the brightness is 1/3 the brightness obtained 
when the disc is entirely removed. (4) Each of the surfaces may 
be illuminated by another surface of uniform brightness, which 
then becomes the primary source. By varying the area of this 
primary source, by means of a diaphragm covering it, the bright- 
ness of the second surface may be varied, the brightness varying 
directly as the area of the primary source exposed. 

The most useful type of photometer for direct comparison is 
the Lummer-Brodhun photometer, in which two surfaces of plaster 
or magnesia are illuminated independently from two sources, and 
by an ingenious arrangement of lenses and prisms, a part of one 
surface is seen contiguously to a part of the other surface. 

Flicker photometry, in which the two beams of light are made 
to fall alternately on the same surface, is employed chiefly where 
it is necessary to compare the brightnesses of lights of different 
colors: a difficult procedure in direct comparison. 



142 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

A simpler but less accurate method of direct comparison of 
brightnesses employs Maxwell's discs of a standard "gray" and 
of dead black. Under constant illumination, the brightness of 
such a combination, rotated at a speed above critical frequency, 
will vary directly as the angular width of the "gray." By means 
of two pairs of discs, one small pair superimposed upon a large 
pair on the same rotating spindle, two surfaces of different bright- 
nesses may be made contiguous, and the difference threshold may 
then be measured directly. 

Two differences in brightness, well above the threshold, may 
be compared by using either three or four surfaces. The bright- 
ness difference between surface 1 and surface 2 may be compared 
with the brightness difference between surface 2 and surface 3: 
or the difference between the brightness of surfaces 1 and 2 may 
be compared with the difference between surface 3 and 4. The 
brightnesses may be varied by using Maxwell's discs under uni- 
form illumination, or each surface may be illuminated independ- 
ently, and the brightness of each controlled in any of the four 
ways above described. 

Measurements of color sensitivity may be made accurately by 
the use of spectral light, either by direct vision in the spectro- 
scope, or by projection of spectral light on a diffusing surface, 
such as a plaster of Paris or magnesia surface. The 1ST and IDT 
for the various colors may be determined, and the range limits 
also determined. In work on color blindness, determination of 
the limit of the red end of the spectrum is important. All such 
work requires a purified spectrum, obtained by passing the light 
through two spectrometer systems in succession, and requires a 
high degree of skill. 

DIFFERENCE ThEESHOLDS FOR HUE AND SATURATION 

The difference threshold for color has been measured in a very 
simple way by means of an ordinary spectromometer. A narrow 
slit used in the eye-piece permits the viewing of a narrow band 
in the spectrum. The telescope is set to bring into view any de- 
sired spectral band, and then the telescope is carefully moved in 
either direction until the band just perceptibly different from the 



SOME SENSORY MEASUREMENTS 143 

original band has been passed. A better method is to illuminate 
a white surface by the two spectral colors to be compared, the 
two colors being contiguous, and presented simultaneously. Vary- 
ing results have been obtained, but it seems clear that the differ- 
ence sensitivity is higher at certain points in the spectrum than 
at others. Maximal difference sensitivity, less than 1 /*/*, is found 
at 580 (orange-yellow) and 490 (green-blue), and minimal differ- 
ence sensitivity in the red (4.7 at 650 w and longer) yellow-green, 
(1.88 at 530 /*/*), and pure blue, (2.15 at 450 /*/*), ranging upwards 
to 4 fifi. (Uthoff's measurements). 

This determination of difference sensitivity for colors is exact 
when the compared bands are equated in saturation and bright- 
ness by mixing white light with one or the other, and reducing 
the intensity of one by a rotating disc, smoke glass wedge, or other 
device. 

The difference threshold for saturation might be worked out 
with relatively little difficulty by the systematic adding of differ- 
ent proportions of white light to a color selected as a standard. 
For accurate measurements, a band of spectral color should be 
employed. Measurements have been made, however, by means of 
Maxwell's discs, employing a colored paper and a gray paper of 
equal brightness. Under such conditions, the saturation thresh- 
old measured in degrees of gray added to the color may be as 
low as 1 per cent for certain colors and brightnesses. For a cer- 
tain red at a single brightness, Geissler 80 found that the satura- 
tion DT was lower for low saturation than for high. 

Tests of Color Vision 

Certain practical work on color blindness requires measure- 
ments which shall have a high degree of certainty rather than 
fineness of measure. Such measurements as previously stated we 
call tests. Many tests for the detection of totally and partially 
color blind and color weak persons have been devised, but the per- 
fect test is yet to be sought. Color tests in general fall into four 
classes: (1) Naming-tests, (2) Matching-tests, (3) Pattern-tests, 

^American Journal of Psychology, Vol. 24, 1916, p. 171ff. 



144 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

and (4) The Nela test. All of these depend upon the discrimina- 
tion of color differences which are large for the normal eye. 

1. In naming-tests, such as Nagel's, the reactor is required to 
select from a number of tinted cards, skeins or samples of colored 
worsted or silk, or from a number of colored balls, those having 
approximately the colors indicated to him by name. Thus, he may 
be asked to pick out the greens, the reds, and so on. Or, he may 
be required to name all of a series of colors presented to him, 
This method has little value for the detection of color blindness, 
since the sensitivity to colors is not indicated by the associations 
of words with colors which the reactor may have formed. In many 
cases, individuals whose color-vision is normal, fail to name colors 
correctly; and in some cases, typically color blind persons may 
name correctly the colors they see imperfectly. 

The naming method is, however, of practical importance, since 
the recognition of color is essential in many fields of work. The 
railroad engineer, for example, must not only see red and green 
normally, but must recognize each quickly. That is to say, he must 
have a dependable association of action with each of the two 
colors, and the nature of his verbal association with the colors is 
the index of his practical associations. In short, if the engineer 
could name red and green correctly under all conditions of rail- 
road vision, it would not matter how much their appearance to him 
differs from their appearance to other people. But color blind- 
ness is always a grave hindrance to color discrimination, and hence 
it is essential that color vision itself shall be tested, as well as 
color naming. 

2. Matching-tests were first introduced by Holmgren, and the 
Holmgren test, Wilson test, Jennings test, and many others are 
constructed on the same principles. In such a test, a group of 
colors, and a sample color, are presented to the reactor, and he 
is required to select from the group all those which match the 
sample in hue. Worsteds are used generally for the colors, on 
account of the relative permanence of the dyes, the large range 
of hues obtainable, and the absence of sheen. These tests, when 
the proper colors are used, and when given by experts to reactors 
who perfectly understand the problem, are quite satisfactory for 
the purposes intended. In the hands of inexpert testers, they are 



SOME SENSORY MEASUREMENTS 145 

highly unreliable, and very confusing results are obtained from 
children and from adults who are unfamiliar with the handling of 
colors. Confusion between color differences on the one hand, and 
brightness differences and saturation differences on the other, is 
a common source of trouble; and the uncertainty as to how far 
the reactor is expected to deviate from a perfect match is another 
serious matter. Some persons of normal color vision make as bad 
confusions in these tests as do some who are typically color blind. 

3. In the pattern-tests, neither naming nor matching of colors 
is required. Stilling 's test, which is the best known test of this 
type, consists of charts or plates composed of small discs or dots 
of carefully chosen colors. These dots are so arranged that in 
each chart numbers are formed by series of certain dots, differing 
perceptibly, for persons of normal color vision, in color or bright- 
ness from the surrounding dots. For the color blind, however, 
the dots composing the numbers on certain of the charts are indis- 
tinguishable in color from the surrounding dots, and hence the 
numbers are unrecognizable. This test has the virtue of detect- 
ing cases in which only the center of the eye is color blind, since 
if some of the dots composing the numbers fall on the color blind 
area, the number is unrecognizable. 

The Ishihara test is similar to Stilling 's, but has fewer plates, 
with some in which the numbers are recognizable by the color 
blind, but not by the normal eye. 

Excellent as these tests are in theory, they are unsatisfactory 
for various reasons. It is apparently difficult to print or dye the 
exact color values which will distinguish adequately normal color 
vision from the milder degrees of color weakness, and these from 
the typically color-blind. The tendency of the colors to fade with 
use is also detrimental. These tests are the best of the standard 
tests for adults, but not satisfactory for children. 

4. To avoid color matching difficulties, and yet retain the 
advantages of worsteds, the J. H. U. test was devised. In this 
test, thirteen sample skeins are arranged in a row, from right to 
left, on the far side of the table from the reactor. A large num- 
ber of assorted skeins are heaped on the table, and the reactor is 
required to place each of these in a column under that one of the 



146 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

sample skeins with which it most nearly agrees in color. There 
is, therefore, no question of a perfect match: it is merely a ques- 
tion of finding, for a given skein, which one of the samples agrees 
with it best. After the reactor has arranged all the skeins, he may 
correct the arrangement until he is satisfied. The arrangement 
may then be sewed to a sheet of cardboard for preservation. This 
test is very satisfactory for adults, but requires from one to two 
hours' time for each reactor, and hence is not practical for exten- 
sive testing. 

To avoid the objections to the J. H. U. test, the Nela test was 
devised. In this test, the worsteds are permanently arranged in 
triplets, that is, three skeins side by side. The reactor is required 
to indicate whether the middle skein in each triplet agrees more 
closely in color with the skein at its right or the skein at its left. 
This test is capable of rapid application to children as well as 
adults, and the form now available detects the color weak as well 
as the color blind. 

A color test must be given by an expert, under standardized 
conditions of illumination, and carefully controlled psychological 
conditions, or its results are unreliable. This applies even to the 
best tests yet devised. Variations in the instructions given the 
reactor, and in the routine of the test, produce variations in the 
reactor's judgments. The emotional tone aroused in the reactor 
is also an important factor. Under different lighting conditions, 
even when daylight is used, the colors of the test materials vary, 
because the composition of daylight varies. When tests are given 
carelessly or unintelligently, not only are confused results 
obtained, but also some normal individuals are made to appear 
color blind, and some color blind appear normal. 

Certain measurements are useful as an auxiliary to tests of 
color blindness, and are of further importance as means of study- 
ing the conditions of these defects. For the red-green blind, the 
relative brightness of the various parts of the spectrum from red 
to blue-green differ from that of the normal eye. For the pro- 
tanope, whose spectrum is shorter at the "red" end than for the 
normal eye, the visible "red" is relatively darker, as compared 
with the "yellow" or "green" than it is for the normal eye. 
Hence, by comparing the relative brightness of red and green 



SOME SENSORY MEASUREMENTS 147 

light for a red-green blind individual, it may be determined 
whether he is a protanope or deuteranope, even though no spectral 
light apparatus be available. For this purpose, a red and a green 
light, using colored glass or gelatine, are so arranged that the 
intensity of the green may be reduced either by graded series of 
smoked glasses, or by an episkotister. The green, at first much 
brighter than the red, is reduced until it seems just equal in bright- 
ness to the red. Measurements are made on normal eyes to stand- 
ardize the scale of reduction, and the protanope may then be 
detected by the considerably greater reduction of the green- 
brightness required for a brightness match for his eye. 

Since the protanope and deuteranope alike see only one hue 
from the "red" end of the spectrum up to the beginning of the 
blue-green, any spectral color within this range may be matched 
by any other in the same range, by proper control of the bright- 
ness and saturation of each. In using the spectroscope for meas- 
urement of these matches, it is necessary to have a means of 
reducing the brightness of the normally brighter of the colors 
employed, and for adding a little "white" light to either. Since, 
however, the colors seen from E to B Gr by the red-green blind 
are really combinations of R and C in balanced ratio, addition 
of blue is exactly equivalent to the adding of white. 

If spectral light is not available, measurements may be made 
with Maxwell's discs of colored paper. Measurements of the rela- 
tive angular amounts of two colors (e. g., R and G) required to 
match a third (e. g., yellow), may be made in normal persons, 
and compared with the measurements on color blind, using the 
same colors. D and W must, of course, be used to equalize satura- 
tion and brightness. In this particular case, the results are not 
so simple as they appear, since for the normal eye the equation 
of R plus G with Y is a color match, complicated by brightness 
and saturation differences, but for the dichromat it is a bright- 
ness and saturation match only, since practically all mixtures of 
R and G are the same color to him. 81 



81 A striking comparison of normal with dichromatic vision may be made with two 
combinations of Maxwell's discs, one of orange-yellow with black and white, the other 
with either red or yellowish- green and black and. white. With proper angular propor- 
tions, the combination may be made to match perfectly in color, for the protanope 
or deuteranope, but of course not for the normal eye. 



148 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

§4. Auditory measurements. 

Measurements of auditory functions are concerned with sensi- 
tivity in the auditory range, and with pitch discrimination; which 
latter is analogous to acuity of vision. 

Instruments for the measurement of auditory sensitivity are 
called acumeters (sometimes, improperly, "audiometers"). These 
are of two types: noise-instruments and tone-instruments. 

The noise-acumeters depend upon the sound of a falling ball 
or falling hammer, striking on a surface of ivory, metal or other 
hard substance. In some instruments, the sound intensity is varied 
by varying the height from which the ball or hammer falls, the 
instrument being kept at a standard distance from the ear. The 
measurements are made directly in terms of the height, in milli- 
meters, of the drop of the ball or hammer. In other instruments, 
such as the Politzer acumeter, the height of fall is kept constant, 
and the distance from the ear varied. These instruments are use- 
ful for the detection of gross deafness of a general sort, but not 
for detection of slight defects, or the comparison of normal capaci- 
ties. It is almost impossible to measure the sensitivity of a normal 
ear by such an instrument, since the absolute distance of the just 
perceptible drop of the smallest ball easily handled is very minute, 
for distances of a few yards from ear to instrument. Attempts 
to use greater height of fall, by removing the instrument to a 
greater distance from the ear, (100 to 200 feet would be neces- 
sary) introduces distractions which make the results quite unre- 
liable. 

The noise-acumeter would not be completely satisfactory, even 
if it were technically practicable. The noise includes a large num- 
ber of simple tones, and there is no way of determining which of 
these components is heard, when the total noise is just above the 
threshold. It is known that sensitivity can be abnormally low 
in one part of the total range of auditory pitches, and normal or 
even hypernormal in other parts of the range. Hence, it is neces- 
sary to devise an acumeter, or a series of acumeters which will 
measure the sensitivity at different points in the range, that is; 
which will employ pure tones. Several investigators are now 
engaged in the attempt to develop such an acumeter, and success 
will undoubtedly be attained before long. 



SOME SENSORY MEASUREMENTS 149 

Acumetric tests are sometimes made by finding the distance 
at which words, or whispers, are audible. These tests are com- 
petent only to discover cases of extreme deafness, and are unre- 
liable for other purposes. 82 It is impossible to give vocal stimuli 
of uniform intensity; and different syllables have different degrees 
of intelligibility. Such tests are best conducted out of doors, for 
indoors a word will often be more audible at a greater distance 
than at certain nearer distances, on account of sound-reflections 
from walls. Even with these objections overcome, the tests would 
not be of sensitivity solely, but of mixed sensitivity and acuity, 
since pitch differences enter largely into the discrimination of 
words. 

The limits of tone (pitch) perception are measured by means 
of large tuning forks for the lower limit, and Konig's bars for 
the upper limits. The forks are adjustable for vibration rates 
from 16 to 64, by steps of single vibrations, the most useful set 
consisting of three forks, each adjustable by means of sliding 
weights, for a part of the total range. Measurement consists in 
finding the slowest vibration rate at which a tone (as distinguished 
from a series of puffs) is audible, and the fastest rate at which 
the tone is inaudible, the mean being taken as the threshold. The 
observation on very low tones is difficult, and the technique is 
not yet fully perfected. For the normal ear, the limit is certainly 
not lower than 16 vibrations per second, and not above 32. 

The Kbnig's cylinders used to measure the upper limits of 
tone perception are usually tuned to vibrate, when struck with 
a steel hammer, in the pitches of the diatonic scale from c 4 = 4,096 
v. s. to c 7 = 32,768 v. s. 83 This range is adequate for adults, 
almost none of whom can hear tones as high as 25,000 v. s., but 



82See Andrews, American Journal of Psychology, Vol. 15, pp. 14-56. 

ssThe abbreviation v. s. means vibrations per second, where a "vibration" is under- 
stood to be the movement of an air particle, or any vibrating object, such as the prong 
of a tuning fork, from the point of rest (£. e., the center of oscillation) to the 
extreme limit of its movement in one direction; back through the resting point to 
the extreme limit of movement in the other direction; and back to the resting point 
again. Unfortunately, in the French system of numbering vibrations, a ' ' vibration ' ' 
is the movement from the point of rest to one extreme, and back to the center again, 
which is just half of the total vibration as we count it. Hence, a fork marked 
' ' 512 v.s. ' ' in the French system is really only 256 in our system. To avoid this 
confusion, some authors write "d. v." (double vibrations) instead of v.s., when they 
wish to indicate complete vibrations. 



150 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

children can frequently hear the highest note of the set. For prac- 
tical testing purposes, the set is quite adequate. 

The method of measurement consists in striking the bars in 
succession, and requiring the reactor to tell whether he hears, or 
does not hear, the note of the bar. Brief preliminary training 
in discriminating the tone from the " click" of the blow is required, 
and careful technique, not only in sounding the bars, but also in 
securing proper conditions of attention, are essential. In expert 
hands, the upper pitch limit, in the scale of the instrument, can 
be determined both quickly and certainly, even in the case of a 
child. The determination is important, especially on children, 
since many who are normal in sensitivity for low pitches, are deaf 
for high pitches (that is, have an abnormally low upper pitch 
limit). Although they can hear words, they have difficulty, on 
account of this defect, in distinguishing words, because the con- 
sonants are obscure, since the characteristic sounds of the con- 
sonants depend upon the relatively high partials in their total 
sounds. It is characteristic of such auditory defectives, that they 
can understand whispered conversation very imperfectly, since 
whispers employ consonants without vowels. 

Galton's whistle, a short pipe with an adjustable plunger, giv- 
ing a gradation of shrill tones, has been used for the determina- 
tion of the upper pitch limit, but its use is now generally aban- 
doned because of its essential unreliability, even in the improved 
form designed by Edelmann. 

For measurements of pitch discrimination, tuning forks are 
used. Two forks, mounted on resonant cases, are necessary, one 
(the variable) being provided with sliding weights, and scaled so 
that by proper setting of the weight it can be put exactly in tune 
with the other fork (the standard), or can be made higher or 
lower in pitch. By the use of carefully controlled technique, the 
thresholds for pitch difference above and below the standard may 
be determined in terms of the scale of weight-position, and the 
actual pitches corresponding to such scale readings may be deter- 
mined by the simple procedure of counting the beats per second. 

A variant instrumentation for pitch difference threshold deter- 
mination provides for the use of a standard fork, and a series of 
forks varying by determinate steps above and below the standard. 



SOME SENSORY MEASUREMENTS 151 

Instead of having to adjust a "variable" fork to a determinate 
pitch, as in the procedure described above, the fork of the required 
pitch is selected from the series. This instrumentation is not 
recommended. With either set of forks, the essential procedure 
is the same. The "standard" is sounded, and then the "vari- 
able," after which the reactor is required to judge whether the 
"variable" was higher than, lower than, or equal, to the "stand- 
ard." Although apparently simple, accurate determination of 
pitch difference acuity requires an elaborate and careful technique, 
which would be tedious to describe here. 

Measurements of Absolute Pitch 

The criteria of "absolute pitch" are somewhat vague. What 
is ordinarily considered as absolute pitch is the ability to name 
correctly a note struck on a well tuned piano, or other musical 
instrument, when the person tested has not heard or produced a 
musical tone for several hours preceding. In this case, the 
accuracy of judgment required is within one semitone. Whether 
in the cases of "absolute pitch" reported, the individual could 
distinguish a slightly flatted or sharped note from the true note 
in the system to which the. individual is accustomed is not clear. 
Further work on such cases, with notes of pitch varying by differ- 
ent amounts from the pitches of the accustomed musical standards, 
need to be made. 

Sometimes "absolute pitch" is understood as the ability to 
recognize the approximate pitches of successive notes sounded at 
random on a musical instrument. In one reported investigation, 
as many as 50 notes were given in a single series or test. In 
such a test, if the first note is correctly judged, the remainder 
could be estimated by relative pitch; and in any case, relative 
estimation, that is, ordinary musical pitch estimation, is a large 
factor in work by this method. 

§5. Measurements of dermal sensitivity. 

Touch sensitivity is measured in terms of the pressure exerted 
on a unit area of skin. Small weights of cork and other substances 
have been employed, but the most satisfactory procedure makes 
use of the Von Frey Esthesiometer. This consists of a horse-hair, 



152 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

fixed in a handle at one end, so that the other end of the hair can 
conveniently be applied vertically to the skin. If such an esthesi- 
ometer is applied carefully, with pressure jnst sufficient to bend 
the hair slightly out of line, the pressure exerted on the skin is 
approximately standard, slight difference in the bending of the 
hair being of negligible effect. The pressure exerted may be meas- 
ured by applying the hair, in a similar manner, to one pan of 
a delicate balance, shortening the hair until it gives the exact 
pressure desired. A series of such esthesiometers, covering the 
desired range of pressure by determinate steps, furnishes the 
means for threshold measurement. Sometimes a single esthesi- 
ometer, with a hair so inserted in a sleeve that the exposed por- 
tion of the hair may be shortened or lengthened at will, and the 
length read on a scale in millimeters, is employed. 

In using either weights or the Yon Frey esthesiometer, great 
care must be used in applying the pressure, as the force of the 
impact varies with the speed. A "weak" hair, forcibly applied, 
may be felt when a stirrer hair, carefully pressed down, will not, 
although the final pressure may be much greater in the latter 
case. The measurer, therefore, must acquire by practice a rrni- 
form speed of application. Since the dryness or moisture of the 
hair causes considerable change in the pressure exerted with 
minimal bending it is difficult to maintain calibration. Filaments 
of celluloid or some other substance might perhaps be employed 
advantageously. 

For rough tests of pressure sensitivity, when measurements 
are not attempted, a variety of stimulators are employed. Tufts 
of cotton, wool, or camels hair brushes, are perhaps the most satis- 
factory. In the use of such means of stimulation, no distinction 
has been made between touch and tickle. 

Tactual acuity, analogous to visual acuity, is measured by 
stimulating the skin simultaneously by two styli, with slightly 
rounded points, carefully applied. The threshold lies between the 
least separation at which two points are felt as two, and the great- 
est separation at which they are felt as one. The instrument used 
is the two point esthesiometer (formerly called merely an esthesi- 
ometer), which has an adjustment by which the separation of the 
styli can be varied finely, and read directly in millimeters and 



SOME SENSORY MEASUREMENTS 153 

decimals of a millimeter on a vernier or micrometer scale. Great 
care must be exercised, in using this instrument, to make the con- 
tacts simultaneous and uniform in pressure. The technique is 
beset with still graver difficulties on account of the fact that very 
often a single stimulus will be "felt" as two. 

Difference sensitivity for touch is measured by means of the 
kaptometer. This is an instrument consisting of a system of levers 
through which a certain standard weight is applied to a definite 
area of the skin, and can be increased or decreased without jar, 
by the removal of counterbalancing weights of any desired size. 
Such measurements can easily be made on the fingers, hands and 
feet, but application to other surfaces is difficult because the instru- 
ment is cumbersome, and, working through gravity, must operate 
in a fixed position. 

Sensitivity and acuity vary greatly in different skin areas, but 
do not vary together. While both are at a maximum on certain 
areas, such as the lips and finger tips, there are other areas, such 
as the temples, where sensitivity is high, and acuity low. In gen- 
eral, acuity is highest on portions of the skin covering the most 
motile organs (lips and finger tips), and lowest where the motility 
is least, as in the skin of the back. 

Pain sensitivity of the cutaneous and sub-cutaneous tissues is 
measured by means of the algometer, or algesimeter, an instru- 
ment constructed on the principle of a spring dynamometer. A 
button or disc of standard area, on the end of the algesimeter, is 
pushed against the skin, the pressure being steadily increased 
until "pain" is reported by the reactor. The pressure, in grams, 
at the moment of producing pain, is read directly from a scale, 
over which a pointer moves as in a spring balance. For tests 
of pain sensitivity, where no measurements are required, a fine 
needle is commonly used, the point being pressed against the skin 
with approximately standard force. In this way points relatively 
algetic and analgetic may be located. 

Pain sensitivity thus measured varies in different parts of the 
body, being greater where the thickness of the tissues between 
skin and bone is least, as on the joints and on the head. For cer- 
tain areas, for instance the temples, sensitivity is greater in 
females than in males, and decreases with age in both sexes. Feeble 



154 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

minded persons are less sensitive, in general, than normal indi- 
viduals, and the more intelligent "normals" are more sensitive, 
in general, than the less intelligent, although there are many 
exceptions. 

Thermal sensitivity may be determined in two ways: by the 
application of warm or cold objects to the skin; and by the appli- 
cation of radiant heat. The former method is almost exclusively 
used. In the simplest form of the method, Blix cylinders are 
employed. These are cylinders of brass or steel, a few centimeters 
in length, and tapering at the end to a flat surface, 1 mm. in 
diameter. These cylinders are heated, or cooled, by immersing 
in water at the proper temperature; then quickly dried; and the 
end-surface applied to the desired point of the skin. For more 
precise work, a hollow metal instrument, through which water at 
the desired temperature is constantly circulated, is employed. 
With either instrument, the period during which the stimulation 
is employed is important. Stimulations of a certain temperature 
which are ineffective for brief application, may be felt if applied 
for a longer time, presumably because of the transmission of heat 
to or from deeper or laterally distant parts of the tissues. Slight 
differences in duration of application of the stimulation at differ- 
ent points may have much to do with the specific location of the 
so-called "temperature points" on the skin. 

Measurement of kinesthetic and other somatic forms of sensi- 
tivity are complicated and difficult, and a merely general descrip- 
tion of it is unimportant. The thresholds for both passive and 
active movement of joints have been determined, and attempts 
have been made to determine similar thresholds for movements 
of rotation of the head, and for movements of the body as a whole. 
Measurements of difference sensitivity to resistance have been 
made chiefly by means of lifted weights, in terms of the series of 
weights lifted under standard conditions. A set of weights and 
weight-holders well adapted to the determination of resistance 
differences sensed through hand and arm are called Fechner's 
Weights. 

Somatic and kinesthetic thresholds depend upon multiple con- 
ditions. Efficient technique in these fields remains to be developed. 
In the fields of the external senses, many types of measurement 



SOME SENSORY MEASUREMENTS 155 

other than those described have been made, and neAv methods and 
new techniqne are devised as the problems develop. But all 
strictly sensory measurements depend fundamentally upon the 
determination of stimulus thresholds, difference thresholds and 
sensory limits. 

Methods of measuring sensitivity and sensory acuity on ani- 
mals, and on infants and human beings of low intelligence, are 
properly described in treatises on animal psychology, child psy- 
chology and mental deficiency. 



CHAPTER VIII 
THOUGHT AND THOUGHT CONTENT 

§1. Imagination and perception. 

So far we have been considering only sense data and relations 
as perceived. But perception is not the only way in which we 
can be conscious of objects. We can imagine or think of things 
which are not "present to sense." At the present moment, I may 
look at the bine-covered match box on my desk: that is percep- 
tion. Then I may close my eyes and still be conscions of the box: 
that is imagination. 

The terms thought of and thought about are commonly used 
in slightly different applications. When I am conscious of the 
box chiefly as a detached object, rectangular in shape, dark blue 
on the ends and light blue on the sides, and with any other fea- 
tures which, if the box were perceived, could be present in a single 
"act" of perception, I am said to think of, or imagine the box. 
In that case, the relations of which I am conscious are mainly 
between different parts of the object itself. If, on the other hand, 
I am aware of the box as it is related to other objects: as a con- 
tainer for matches; as made from a thin sheet of wood by an 
ingenious machine; as costing, with the contained matches, one 
cent; as inflammable; and so on, I am said to think about the box. 
This difference between thinking of and thinking about will be 
more fully considered in a later section of this chapter. 

Imagination and perception are closely related. In general, it 
is possible to imagine only what has been perceived previously. 
The medieval philosophers, from whom "common sense" theories 
are so largely drawn, held that the dependence is absolute. 
"Nothing," they said, "can be in thought which has not previ- 
ously been in perception. ' ' Whether this sweeping generalization 
is or is not justified, Ave shall not attempt to decide until we have 
considered the important topic of instinct: but certainly there is 
some truth in it. The adult who has been blind from birth can- 

156 



THOUGHT AND THOUGHT CONTENT 157 

not imagine light and color; the congenitally deaf man cannot 
imagine musical tones; and the anosphresic man cannot imagine 
the odors of flowers. Yet, as we shall see, constrnctive imagina- 
tion is possible. An intelligent man who has never seen snow may 
be able to imagine it, if he has perceived cold, and white objects, 
and has noticed the differences between wet and dry objects, and 
has observed the possibilities of changing the characteristics of 
an object. Furthermore, men have succeeded in imagining things 
— such as the unicorn and the sea serpent — which no man has ever 
perceived. 

On account of the close relation of imagination and perception, 
it has been customary to divide the topic into the same modal 
classes as the senses. Visual imagination is the imagination of 
objects which, if perceived, are predominantly visual: that is, those 
which include colors and brightnesses among their characteristics. 
The thought of sounds is called auditory imagination; the thought 
of odors, olfactory imagination, and so on. 

Individuals differ in regard to their habits of imagination as 
modally distinguished. Certain persons think of the visible 
details of objects more often, or more clearly, than of their audi- 
tory details, or details of other modes. Certain others think pre- 
dominantly of the auditory details. From the consideration of 
these facts we derive the distinction of imaginative types. The 
predominantly "visual" thinker is said to be of the visual type, 
or a visile. We have, then, theoretically at least, the visile, the 
audile, the tactile, the gustile, olfactile, motile, (kinesthetic) and 
other modal classes of imagination. Although no one would be 
supposed to belong strictly to one of these classes, but rather to 
imagine one of these sorts of sense data with greater ease, or fre- 
quency, or vividness than the others, the distinction has consider- 
able theoretical interest. 

We understand, then, as belonging to a certain modal "type 
of imagination;" as, for example, the "audile;" the person who 
either (a) imagines 1 " sounds more vividly than he imagines other 
sense data, or who (b) in thinking of an object which combines 
auditory data with other data, tends to think of the auditory data 
rather than the others. These tendencies apparently depend upon 
the capacities of sense perception, either in regard to sensitivity 



158 ELEMENTS OE SCIENTIFIC PSYCHOLOGY 

and acuity, or upon habits of sensory attention. The man who, 
with all his senses normally efficient, habitually attends to visual 
features of the world, to the relative neglect of the other features, 
will, in his thinking, follow the same lines of habit, and be a visile. 
The man who is distinctly defective in some sense will not be of 
the imaginative type of that sense. If he is, and for a large part 
of his life has been visually defective, he will not be a visile, 
since he will attend more strongly to the other sense data, and 
will discriminate them more effectively. Or, we may put the facts 
in another form, and say that the person who is defective in any 
of his senses will not be highly developed in imagination of the 
corresponding mode: but nevertheless a man may have normal 
efficiency of a given sense, and yet neglect it perceptually and 
imaginatively. 

The modes of imagination which are most highly developed, 
among people at large, are, as we would expect, the auditory, 
visual and kinesthetic; the modes in which perception is most com- 
plex and most highly developed. Taste, smell and touch, on the 
other hand, which are of less practical importance in civilized life, 
and in w^hich, for the average person, perceptual discrimination 
is least developed, are the modes generally neglected in imagina- 
tion. 84 

§2. Reproductive and productive imagination. 

In imagining an object or an event, one may be thinking of a 
real object, which he has earlier experienced perceptually; or of 
an event which actually occurred in the range of his perception. 
Thus, I may imagine the flaming red automobile which buzzed by 
my window a few moments ago. I may imagine its color, form, 

84The term imagination is derived from image, a copy. Some of the ancient GreeK 
philosophers supposed thought to be possible through the operation of copies of objects 
(eidola) which, although of extremely rarefied substance, yet preserved the form and 
many other characteristics of the objects from which they "emanated." These 
"eidola," floating about in the air, enter the brain on occasions, and are then objects 
of consciousness — ideas. This image-doctrine has persisted for several thousands of 
years, and even now it is widely believed that such "copies" of real objects exist, 
and that it is such a copy or copies of which one is conscious in imagination. As 
the doctrine of "images" is held at present, the images are not supposed to be of 
the same substance as the original object, but of a sort of mental stuff, which can 
imitate the aspects of reality. 

No such "mental images" are assumed in the discussions of this book. 



THOUGHT AND THOUGHT CONTENT 159 

noise and passengers; and I may think also of the sequence of 
its passage : first the noise, faint in the beginning, and then londer, 
followed by the visible appearance; its turn at the corner, and 
subsequent disappearance. Now, if in my thinking, I follow the 
details as they occurred, although many may be omitted in my 
thoughts, the thinking is called reproductive imagination. The 
consciousness and conscious processes (not the content, or object) 
of the primary perceptual experience are ' ' reproduced ' ' in imagi- 
native form. 

I may, however, imagine the passing of the car in a way which 
did not actually occur. I can imagine the car approaching as it 
did, but appearing a dark green. I can imagine it stopping under 
my window, and two men alighting, who come to the window, ask 
about the road to the next town, and then re-enter the car, which 
drives on. This type is Productive, or Creative Imagination. As 
in the illustration given, it always has a basis in past experience. 
That is, it has a foundation in reproductive imagination. Experi- 
ences of the past are reproduced, but with changes in the time- 
order, and in the space-order, and in other relations. 

In a general way, creative imagination may be described as 
the re-combination of elements of former experiences: the ele- 
ments, or certain unit combinations thereof, are reproduced as 
parts, and the creative function consists solely in the re-combina- 
tion. An old illustration may be given. In imagining a harpy, 
the body of a vulture is thought of, with the face of a woman. 
Both of these features are "reproduced." Both have been per- 
ceived. The combination of the two, however, for the man who 
invented the harpy, was ' ' creative. ' ' 

If we should apply the scholastic doctrine "nothing can be in 
thought which has not first been in perception, ' ' we should incline 
to say that the above description of creative imagination as a 
mosaic or synthesis of reproduced fragments is final. We must 
refuse to accept this simple explanation for two reasons: first, in 
the combination of reproduced factors, something more than 
mosaic, or patch work, results. The fragments are adapted to 
the purpose, and so modified, in order to produce a coherent whole, 
that in some cases no items can be found which precisely repro- 
duce any of the parts of former experiences from which they are 



160 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

drawn. Second, it is by no means certain that new materials, 
previously nnperceived, may not be imagined. The definite facts 
of instinctive, unlearned reactions compel ns to hold this view as 
possible. Even if no elementary sense data can be perceived with- 
out perceptual experience of them, the combinations of these sense 
data into concrete objects and the related systems of such objects 
may be thought of. 

§3. Memory and anticipation. 

When reproductive imagination occurs, it may involve recog- 
nition. That is, when I imagine some object or event which I 
previously experienced, I may also recognize it as having been 
previously experienced. The recognition may be definite ; the con- 
tent imagined may be referred to a "more or less" definite past 
date. Thus, in imagining the face and voice of a certain person, 
I may identify them as of a person seen-yesterday, or a person 
seen-at-9-o'elock-on-the-4th-of-July. On the other hand, the object 
or event may not be dated at all: I may not be able to identify 
the time except as past. The recognition in this case consists in 
the consciousness of a certain againness. I identify the imagined 
lady as seen at some indefinite time in the past, and nothing more. 
In any case, whether the recognition is definite or indefinite, the 
reproductive imagination with recognition is properly called 
memory. 

The element of againness in indefinite recognition is obviously 
a relation of a simple temporal sort. In definite recognition, the 
time relation is more complex, and the relation of betweenness, 
with perhaps other temporal details, enters. But the recognition 
can become definite in ways other than the temporal. For 
example, the lady of my imagination can be recognized as my 
sister: a very complex relational situation is introduced there at 
once, and the content of my imagination is very definite. The 
recognized content may be definite in innumerable ways, but the 
usual relational factors involved, in addition to those of time and 
space, are relations of classification, or inclusion. An object 
(plant, animal, picture, etc.) is recognized as belonging to a cer- 
tain class (rosacae, canine, Flemish school, etc.), the definiteness 
of the recognition depending upon the smallness of the class ; i. e., 



THOUGHT AND THOUGHT CONTENT 161 

the complexity of the relations. While the illustrations just given 
occur most readily in perceptual recognition, they may occur also 
in imagination. 

Recognition in imagination, however complicated by other rela- 
tions, must always involve, and be based upon the again relation. 
Regardless of the defmiteness of the relation of an imagined con- 
tent, it is not recognized (re-cognized) unless it is referred to 
some past experience. 85 

Pre-cognition is just as much a fact as is re-cognition. In the 
latter case, we identify a thought-process with a previous percep- 
tion-process. In the former, we identify a thought-process with 
a future perceptual process. This forward-reference of an act of 
imagination is called anticipation, and differs from the backward- 
reference of recognition only in the time-factor involved. 

The symmetrical nature of recognition and anticipation may 
be shown by very simple cases. Consider in imagination an ice- 
cream soda: it may be in one case thought about as the ice-cream 
soda you felt, tasted, smelled, swallowed and paid for an hour 
ago: in another case, it may be thought of as the one you will 
have an hour hence. The main difference, after all, is that the 
one thought causally depends upon the past perception, whereas 
the other thought causally influences the future perceptions. 

In either case, the imagination may be erroneous. Many recog- 
nitions are false, and so are many anticipations. Not only do we 
fail to recognize in many cases of reproductive imagination, and 
fail to anticipate in many cases where the future actually is fore- 
shadowed; but we anticipate events which never do happen, and 
we recognize events which have not happened. 

One of the most striking types of false recognition in percep- 
tion is that to which the term "illusion of the deja-vu" is con- 
ventionally applied. Often one views a situation: a mountain land- 
scape, a bit of village street, a corner of a room, or what not; a 
situation which he could not possibly have seen before; and yet 
he recognizes it. "Why, I have been here before! I have seen 
this before!" And yet the recognition is false. The same sort 



S5ln the case of perceptual recognition, the usage of language is sometimes looser. 
Thus, in seeing a picture which one has never seen before, he may say that he "recog- 
nizes " it is a Rembrandt. But he means, really, that he recognizes certain details 
Avhich he has previously perceived in other works of Rembrandt. 



162 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

of false recognition of spoken words also occurs. In some cases, 
it is possible that the words have been heard before, and cannot 
be definitely recognized; in other cases, it is impossible to escape 
the conclusion that the recognition is erroneous. 

Failure to recognize what is actually reproduced is a common 
affair. It reaches its most striking phase in unintentional pla- 
giarism, where an author or dramatist imagines a plot, or a setting, 
or some significant details, without recognizing them as something 
he has read or seen. Of course, deliberate plagiarism does occur : 
and, moreover, striking coincidences have happened. Two com- 
posers might invent the same melody independently. But cases 
of coincidence and of deliberate imitation are undoubtedly infre- 
quent as compared with failure to recognize. 

§4. Images, ideas and concepts. 

The content of which one thinks at any time may be a rela- 
tively simple object, such as a lead pencil, in which only the sense 
data and intrinsic relations are attended to. By intrinsic relations 
we mean those which subsist between parts of the object itself; 
whereas extrinsic relations subsist between the object and other 
objects. The content of such a thought, in which sense data and 
intrinsic relations alone are attended to, is called, in conventional 
terms, an image. It must be remembered that an "image" is not 
a thing; not a "copy" of some more "real" object: but is merely 
an abstract term for whatever content, of the designated sort, 
happens to be thought of at a given time. 

In most thinking, however, extrinsic relations are involved 
along with the central content. A pencil is seldom thought of 
merely as a hexagonal form (or a cylinder) ; yellow (or some other 
color), on the surface; and tapering at one end to a black point. 
It is usually thought of as something to write with: which involves 
relations to arm movements, tables, paper and black marks. In 
this case, we have what is called an idea, rather than an image. 
An idea may accordingly be defined as a definite object thought 
about as related to other objects. 86 

& 6 Some confusion is inevitable here, since the term "idea" is also applied to the 
thought, or consciousness, as well as to the content. In the case of the Concept, or 
General Idea, there is fortunately no such confusion, since the term "concept" is, 
and has always been, applied to the content, never to the consciousness. 



THOUGHT AND THOUGHT CONTENT 163 

The emphasis upon extrinsic relations, evidenced in the idea 
as compared with the image, may be carried to an extreme in 
which intrinsic relations, and sense data, are relatively insignifi- 
cant. In thinking about "pencil," for instance, I may attend 
only slightly to color, shape, or size of such an object, but attend 
to the extrinsic relations which any pencil will have : the essential 
relations to arm movements, writing surface, and black marks. 
The content in this case is a general idea or concept, and the act 
of thinking of a concept is conceiving. 

The unfortunate confusion over the nature of images, which 
still persists in some psychological discussions, may be made less 
dangerous if we compare it with the earlier confusion over the 
nature of the concept, embodied in the philosophical discussions 
of the middle ages. Certain philosophers maintained that the con- 
cept or ' ' Universal, " as it was called, was a real thing. That, for 
example, there was a real Universal Table, in addition to the 
innumerable individual tables: otherwise, it was asked, how could 
one think of "table in general" rather than of some particular 
table of a definite color, size, and number of legs? How, further, 
can we think of Man, instead of just some particular man, unless 
Man actually exists! Other philosophers went to the opposite 
extreme and declared the universal to be a mere name, capable 
of being applied to a wide range of particular individuals. 

Of course, there is truth — incomplete — in both extreme views, 
but both were over-stated. The concept is an actual fact: a real 
system of relations, although not a thing: and the name we give 
a concept (whether a concept of Man or a Table) designates a 
system of relations applicable to a number of particular objects. 
Now, the "image" has just as much reality as the concept, and 
no more. The image is not a thing, distinct from physical things, 
but is some object, or objects, as thought of. The green creeper 
and the red bricks which I now see through my window are real 
objects: but when I close my eyes and imagine them, the same 
identical creeper and bricks are called images; which means merely 
that now they are imagined or thought about, instead of being per- 
ceived. If this point is considered with sufficient care, we shall 
not be in danger of accepting the popular view of "images" and 



164 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

" ideas" as a special kind of object, existing in the mind as does 
furniture in a parlor. 

Since, after all, the difference between image and idea, and 
between idea and concept, are matters of degree, in spite of 
the considerable difference between image and concept, dne to 
the relative importance of the sensory content in the former, it 
is a useful custom to use the word "idea" generally for all three, 
to avoid the repetition of "image, idea, and concept" when we 
wish to include all these types. Hereafter, therefore, where the 
term "idea" is used without qualification, it will indicate any or 
all three types of thought content, as the case may be. 

§5. Symbolic thinking. 

Much thinking goes on without ideas being thought of. If I 
am asked "what weed is burned for the purpose of inhaling the 
smoke," I reply "tobacco," and have neither image, idea or con- 
cept, of the plant or its products. From that point I can go on , 
through a consideration of the agricultural, economic, and physio- 
logical aspects of tobacco-growing and us^, merely using words 
with very little more thought-content than is involved in the first 
step. Ideas do occur, however, at various points in this think- 
ing process, and at any point I could break the chain, and sub- 
stitute ideas for words. In general, it is more efficient to depend 
upon words as fully as possible. 

This sort of thinking, by the use of words or other equivalent 
acts, is symbolic thinking. The essential principle involved is 
exactly the same as in an algebra problem, where w may stand 
for sheep, y for horses, and z for calves; and if these symbols are 
used in a regular way, we proceed as far as necessary with no 
further attention to the things they represent. The detailed nature 
of symbolic thinking cannot be understood until reactions and 
habit formation have been discussed. The topic is introduced at 
this point so that the acute reader of the section on ideas may not 
misunderstand the presentation given therein. 

§6. The determination of imaginative types. 

In the past, much interest has attached to the problem of deter- 
mining the predominant imagination-types of individuals. This 
work, of course, belongs to Individual Psychology, but has re- 



THOUGHT AND THOUGHT CONTENT 165 

ceived serious attention from a number of general psychologists, 
chiefly because of its intrinsic fascination to the man of scientific 
curiosity. It has received very little attention from the workers 
in strictly Individual Psychology, because in the first place, there 
is no practical use which could be made of the determinations, if 
such determinations were possible (workers in mental measure- 
ments are for the most part persons of intensely practical bent) ; 
and secondly, because, unfortunately, accurate determination has 
not been found possible. 

Several test-methods have been proposed, the one most largely 
used being the direct observation method of Francis Galton, who 
was the first to become interested in this problem as he was in 
several other problems of individual psychology. Because the 
method usually requires the answering of a carefully drawn set 
of questions, it is sometimes called the "questionary method," 
but this term is not accurately descriptive. 

A series of observations illustrative of the method may be made 
as follows: 87 

First Method. Simple Eeport. 

Imagine a pan of onions frying on a stove: 

(a) Can you see the onions in imagination'? What color are 
they? What sort of a pan can you see? In what position does it 
sit on the stove? Are you sure you sec the details described, or 
do you think them in words, or in some other way? 

(b) Can you hear the onions sizzling in the pan? 

(c) Can you smell the odor of the onions? 

(d) Imagine some of the onions put into your mouth. Can 
you feel (tactually) them? Are they sensorially hot? Are they 
salty, or do they need salt? Can you imagine them as overly 
salted, and taste the salt? 

(e) Imagine yourself grasping the handle of the frying pan 
to lift it off of the stove. Can you "feel" the handle (tactually: 
thermally) ? 

(f) Do you "feel" the shape of the handle? The weight of 
the pan and contents? 

87 For a longer and more detailed set of instructions and questions, see Titchener, 

Experimental Psychology, Student's Manual, Qualitative, §51. 



166 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

(g) Think (imagine) the word "onions." Do yon hear it? 
See it (in written or printed form) 1 Or feel it (feel the saying 
of the word) ? 

The observations demanded by such a set of instrnctions and 
questions are apparently simple, and it may seem a simple matter 
to obtain accurate answers to the questions. Bnt in reality, very 
complex processes are involved in the observations, and it is dif- 
ficult to obtain reliable information in this way. The whole matter 
of reaction and habit formation needs to be understood before we 
can even explain how it is possible to obtain an accurate report 
on any observation; and these observations offer as great diffi- 
culty for accurate reporting as any we are called upon to make. 
Mere practice in such attempts at analysis, instead of increasing 
the accuracy, uniformly decrease it. Experimental attack is neces- 
sary to indicate the sources of error. The following set of instruc- 
tions will help to illustrate. 

1. In imagining the visual aspect of a pan of onions, try (a) 
with exact fixation of the eyes on a point on the wall, (b) with 
no restraint on the fixation, neglecting the eye movements. In 
which way can you "see" the onions best? 

2. In imagining the odor of the onions, (a) hold the breath, 
or else, having taken a deep breath, let it slowly out as you try 
to imagine the smell, (b) instead of holding the breath, or exhal- 
ing "sniff" i. e., inhale sharply with constriction of the nostrils. 
With which method is the odor imagined most clearly? 

3. In trying to imagine the taste, heat, and touch of the onions 
in the mouth, (a) depress the tongue and hold the lips and cheeks 
rigid; (b) allow the mouth, lips, and tongue to move without 
restraint. Which method gives the best results? 

4. In imagining the "feel" of the pan handle, and weight of 
the pan, (a) hold the hand and arm rigid; (b) let the hand and 
arm be at ease. Can the "feel" and weight be imagined as readily 
in the first case as in the second? 

5. In imagining the word "onions," if it seems "visual" 
when no eye restraint is employed, try the effects of fixation. If 
it seems audible, try rigidity of the mouth, tongue and vocal cords: 
or put the vocal organs in the position of saying a (as in rat), and 
try to imagine the word under such conditions. 



THOUGHT AND THOUGHT CONTENT 167 

6. When imagining sounds which seem clearly "heard" in 
imagination, observe whether there are distinct changes in ten- 
sion in the mnscles within the (middle) ear. 

7. Observe carefully the vocal accompaniments of the imagin- 
ing of visual, olfactory and other sensory details. Also, inhibit 
vocal movements in such cases, as instructed under (5) above. 

As a result of such observations, the following conclusions will 
be strongly suggested: 

I. The "visual," "auditory," "olfactory" and "gustatory" 
characteristics of objects imagined are to a considerable extent 
due to kinesthetic processes involved in adjustment of the corre- 
sponding sense organs. The "visual" characteristics, for example, 
are due to adjustments of the eye as if seeing: the "olfactory" 
characteristic to adjustment of the breathing and nasal muscles 
as if smelling, and so on. 

II. Kinesthetic processes are highly important in verbal 
imaginations. The words are "thought" through processes involv- 
ing actual slight movements of the vocal organs. 

III. In many cases, imagination of various apparent modal- 
ities turns out to be verbal thought accompanied by sense organ 
adjustments as described under I. In other cases, movements of 
the arms, legs, fingers, or other parts of the striped muscular 
mechanism are involved. 

Second Method. Veebal Style 

It has been supposed that the writings of an author may give 
a clue to his imagination-type. Poe, who used sound words so 
lavishly (see The Bells), is supposed, therefore, to have been of 
the audible type. Other authors, ayIio seldom describe or men- 
tion sounds, but revel in visual description, are supposed to be of 
the visile type. An author who uses names of odors, who refers 
to odor perception, and who describes odorous substances copi- 
ously, would be said to be of the olfactile type. 

While it is true that the material used by an author indicates 
the lines of his interests in a general way; that one who writes 
much about color, for instance, is keenly interested in color, and 
influenced greatly by color perception; this gives no information 



168 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

as to liow the author thinks of the sensuous data in which he is 
so interested. Poe may have thought of sounds in a purely verbal 
way, and Amy Lowell may think of colors and visual objects in 
the same verbal manner. 

Thied Method 

This method attempts to obtain more accurate reports, by pre- 
senting material to the reactor for memorization for a specific 
length of time, in order that a report may be made on the proc- 
esses occurring during perception as well as during recall. In 
one form of this method, letters, arranged in regular rows and 
columns, are presented (as in Binet's Letter Square Method), and 
the R is required to learn the letters, and to reproduce them after- 
wards in the original arrangement, if possible. R is required to 
report on his method of learning, and on the "images" in recall- 
ing. Sometimes inferences as to the efficiency of visual imagina- 
tion are made also from the tendency of R to recall letters cor- 
rectly, but to place them incorrectly, on the assumption that with 
good visualization of the whole group, the letters will be "seen" 
in their proper place, if at all. 

In other forms of this method, words, geometrical figures, 
colors, and various diagrams and pictures are presented; or words 
and tones presented acoustically; or tactual, thermal, algetic and 
kinesthetic impressions produced; as a basis for report. This 
method has the virtue of being experimental, and may, perhaps, 
give more reliable results than does simple imaginative observa- 
tion, although many of the same sources of error are present. 

§7. The cultivation of imagination. 

It might be supposed that the determination of imagination 
types would have a certain practical value, in addition to its attrac- 
tion for mere psychological curiosity. It has been assumed, 
indeed, to be important to determine the type of an individual, 
especially a child or adolescent, in order, first, that material for 
learning (school material, for example), should be presented to 
the sense (vision or audition) in which the thought-facility of the 
individual is greatest; and, second, that training in imagination 
might be given in the modes in which the individual is deficient. 



THOUGHT AND THOUGHT CONTENT 169 

The first proposed application of type-determination, even if 
possible, would be a round about way of getting at something 
which can.be more simply approached. The practical question as 
to which method of presentation, visual or auditory, best suits the 
child's needs, can be determined only by finding in which way 
the child actually learns best, by testing him for speed and 
accuracy of learning, as well as for retention; and not by bother- 
ing about the sort of "imagery" he uses in reproducing. 

As regards the second point: the dependence of imagination 
upon perception is such (as will be shown in later chapters) that 
the only way of increasing the facility of thought of any class of 
sense data is to increase the attention to and the discrimination of 
that sort of data in perception. 

Determination of the modality of imagination is useful in order 
to discover the habits of perception upon which imagination is 
based. But in any case, it is a determination simply of the kind 
of objects one thinks about, and not of how one thinks of them. 
The latter question can be answered only by a thorough analysis 
of the process of reaction and habit-formation, not by simple obser- 
vation or so-called "introspection." It is the confusion of these 
two problems which has in the first place made the topic of types 
of imagination seem unduly important, and in the second place, 
made it seem unduly complicated and hopeless of solution. 



CHAPTER IX 
THE BODILY MECHANISM 

§1. The complex organism a social group. 

The body of a human being is made np of a vast number of 
cells, together with certain structures and fluids manufactured by 
certain groups of these cells. Among these manufactured prod- 
ucts are bone, cartilage, hair, nails, the lymph and the plasma 
of the blood. The cells are living; the structures and fluids men- 
tioned are non-living, but are essential to the life of the body, 
and the life of its cells. 

The relations between the cells and the cell-products which 
make up the body are strikingly like those existing in a swarm 
of bees. The bone, hair, lymph and other non-living parts of the 
body may be likened to the combs, honey, and bee bread: the 
individual cells to the bees. Each cell in the body is a distinct, 
living individual: it could, if proper conditions of food, moisture 
and temperature were supplied, remain alive and even grow, 
although isolated from the other cells. In fact, cells from lower 
animals have been kept alive, and have thrived, in artificial cul- 
tures. So a bee may live when separated from the swarm. 

Under ordinary conditions, however, the life of the bee depends 
upon its being a part of a swarm; and the life of a cell depends 
upon its being a part of an animal body. The swarm is made up 
of groups of individuals having functions which are contributory 
to the life of the whole swarm, although no one group performs all 
the necessary functions. The queen, after fertilization, deposits 
eggs in cells prepared by the workers and does nothing else, except 
maintain her own vital functions. Certain workers care for the eggs 
and larvae; others gather honey or pollen; others prepare the "bee 
bread;" and others make and care for the comb. The labor of 
each group so supplements the labor of the others that the total 
functions necessary for the life of the swarm are accomplished. 

In a similar, but more highly specialized way, the various 

170 



THE BODILY MECHANISM 171 

kinds of cells in the animal body perform functions wliicli mutually 
supplement one another. Some cells merely protect the body from 
outside forces; some secrete saliva; some manufacture gastric 
juice ; still others elaborate other digestive fluids, which are 
needed to transform food which has been eaten into materials to 
nourish the whole array of cells. Certain cells, (muscle cells) 
merely contract and expand: but in the abeyance of their func- 
tion, digestion, circulation and respiration' could not go on, and 
all the cells in the body would die. Some cells do nothing but 
transmit impulses from one part of the body to another; others 
floating in the blood stream are merely conveyers of oxygen; and 
still others roam about through the body, devouring enemy cells. 
The list of specific, indispensable functions, carried on by special- 
ized cell groups, is a long one. 

All of these cells, with their diverse functions, cooperate in a 
most efficient way, or the whole group perishes. Because of this 
cooperation, the body is an organism or individual, instead of a 
mere colony or mob of minor individuals. Nevertheless the indi- 
vidual cells are the life-units, and the body is a society of these 
individuals; the individuality of the body is just its high degree 
of social organization of the constituent individual cells. 

Just as the organization of individual cells makes up the com- 
plex animal, so does the same sort of organization of insects and 
animals (bees, wolves, or men) make up a still higher individual, 
the swarm, pack, or social group. The relation between a man 
and the constituent cells in his organism is precisely like that 
between the highly trained army division and its constituent men, 
except, that in the animal body there are no commanding cells, 
but the whole is organized as an intricate republic. 

The unity of the complex animal organism lies in its functions. 
Structurally your body is a conglomerate of myriads of units. But 
the whole group act in such interdependent ways that the actions 
become actions of the group as a whole. It is true that there 
is a mental unity connected with the organism, but this again is 
dependent upon the social action of the cells. Consciousness has 
as its organic condition not the function of any particular cells, 
or particular group of cells, but the synthetic or integrative action 
of several large groups of cells. 



172 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

§2. The living cell. 

Every animal, and every plant, is either (1) a single cell, or 
(2) a group of cells, with certain cell products. For the study 
of animal function, therefore, it is necessary to have an elementary 
knowledge of the nature of the cell. 

The substance of the cell is known as protoplasm, and is of 
varied chemical composition, according to the kind of cell. The 
complete cell has a nucleus, or sometimes, as in the striped muscle 
cell, a number of nuclei; from which the remaining protoplasm 
of the cell is distinguished by the name cytoplasm, 88 In many 
cells, a single nucleus is surrounded by a layer of cytoplasm. In 
some, the nuclei lie on the outer surface of the cytoplasm. The 
cytoplasm of various types of cells receives special names : sarco- 
plasm in the muscle cell : neuroplasm in the nerve cell, and so on. 

In complex plants, the cells secrete a substance which forms 
cell walls, enclosing the cells : the formation of these being much 
like the formation of an oyster's shell; and like the shell, the cell 
wall is non-living. In the animal there are no cell walls, but many 
cells are wrapped in delicate connective tissue membranes, which 
are produced, not by the cell so wrapped, but by a special type 
of "connective tissue" cell. 

Cells are of various sizes and forms, but in general microscopic 
in cross section, although some may be (in the human and other 
large animals) several feet in length. Many types of cell in the 
complex animal are of compact shape — cuboidal, or disc-like, or 
of short cylindrical form, or of various irregular shapes approach- 
ing these — and the unicellular plants and animals are most gen- 
erally of compact form. Some of the free-moving unicellular 
organisms have cytoplasmic "hair" or cilia, as do certain "hair 
cells" in the complex organism. Many unicellular animals have 
the power of changing their shape, and so do muscle cells in the 
complex animal. 

In the nucleus is found the chromatin, which is the important 
substance in the hereditary transmission of characters from parent 
cell to "daughter" cells, and. so from organism to organism. 
Growth and development in the cell itself, and the manufacture 



P8Both nucleus and cytoplasm are protoplasm, although in any given cell they differ 
from each other chemically and structurally. 



THE BODILY MECHANISM 173 

of substances to be "secreted" (the secretions of the various 
gland cells, etc.), are controlled by the nucleus. 

Every cell in the complex animal body is descended from a 
single cell: the fertilized egg. In fertilization, the nucleus of a 
spermatozoon or sperm cell (male germ cell) enters the ovum 
(egg) and unites with the nucleus there to form a single nucleus. 
The egg then divides by mitosis, to form two cells; these divide 
in the same way, and so on, each generation doubling the number 
of cells. As the cells become numerous they form first a solid 
mass, the morula; this then enlarges and becomes a hollow ves- 
icle, the blastula. Up to a certain point in this process of cell- 
multiplication, all the cells are exactly alike, and exactly like the 
original fertilized egg. If, for example, the two cells resulting 
from the first division of the fertilized egg are separated without 
injury, each will develop into a complete animal, the two almost 
exactly alike. Even at a later stage, when four, eight, or more 
cells have been produced, division of the mass of cells into two 
groups of equal numbers may, in the case of certain animals, pro- 
duce the same result. So-called "identical twins" are probably 
produced in one of these ways. 

At a certain stage in the development, the cells begin to be 
differentiated; and only a small group retains the likeness and 
potentialities of the original fertilized egg. At what point in 
development this differentiation begins is not certainly known, but 
there is evidence of it in the morula, in which the inner cells seem 
to differ from the outer layer. In the blastula, three types of cells 
are discriminable, and there are undoubtedly more. The three 
types form three germ-layers: the ectoderm (outer layers), endo- 
derm (inner, or lining layer) and the mesoderm, which lies be- 
tween the two, but does not always form a complete layer. 

With continuing multiplication of cells, differentiation of the 
cells increases, and the cell group begins to assume the form of 
an animal. From the fertilized egg through the blastular stage, 
the new animal is known as the embryo; but as it begins to assume 
a form like that of vertebrate animals, it is known as the foetus. 
The human foetus looks not very human at first, but in approxi- 
mately seven months' time the multiplication and differentiation 
of cells has reached the point of producing an infant, capable of 



174 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

independent existence, but not fully prepared for separate life 
until two months later. 

The complete human animal includes essentially cells of nine 
' classes, differing markedly in structure and function. These are: 
muscle cells, nerve cells, gland cells, epithelial cells, connective 
tissue cells, bone cells, cartilage cells, blood cells and germ cells. 
Within these classes there are further almost innumerable impor- 
tant differentiations. These cells are named for the tissues of the 
body in which they are the essential components. But each of 
these tissues actually contains from four to all of the types of 
cells. Blood cells are found in all of the tissues ; connective tissue 
cells, and their products, are necessary parts of glands, muscles 
and nerves ; and nerve cells penetrate muscles, glands, connective 
tissue, cartilage and bones. 

The germ cells in the body are in the testes of the male and 
in the ovaries of the female. They are the only cells not differ- 
entiated in type from the original fertilized egg from which the 
whole body developed. Either in the male or the female, they 
are practically exact copies of the parent cell (the fertilized egg) 
from which the body developed. These germ cells, by a process 
of reduction-division, produce spermatozoa in the male, and eggs 
in the female, which are incapable of reproduction until a sperm 
nucleus penetrates an egg and unites with its nucleus. 

One type of bone cells, osteoblasts, (literally "bone-builders") 
produce bone by secreting it, as an oyster secretes nacre (mother 
of pearl). They work from the center of the bone outwards, and 
are followed by another type of bone cells, the osteoclasts (literally 
"bone destroyers"), which eat the bone, and so render the bones 
hollow. Cartilage cells secrete cartilage in much the same way, 
but as there are no "cartilage eaters," cartilage is solid. 

Blood cells are of two general types: red blood corpuscles 
(erythrocytes), and white blood corpuscles (leucocytes). The 
former are produced by parent cells in the marrow of certain parts 
of the bones. As they soon lose their nuclei, their span of life is 
brief and they arc finally filtered out of the blood and destroyed 
in the spleen. During their life-time they float in the blood stream 
and are mere carriers of oxygen from the lungs to the various 
tissues of the body. White blood corpuscles are of several kinds, 



THE BODILY MECHANISM 175 

but some kinds, at least, are like independent animals, having the 
power of crawling, like the amoeba; and hence they may leave 
the blood stream and penetrate the tissues. These leucocytes 
actively attack bacteria, and devour them. For this reason they 
are called phagocytes (eater-cells). 

Connective tissue cells manufacture and keep in repair the 
fibers and sheets of which connective tissue is largely composed. 
The ligaments which bind the bones together at the joints; the 
tendons which connect muscles to bones ; the fascia (broad sheets 
lying between the skeletal muscles and the superficial tissue — and 
between certain layers of muscles) ; and the mesenteries which sup- 
port the intestines, are strong tough strands and sheets of con- 
nective tissue. The delicate wrappings of nerve cells (neurilemma) 
and of muscle cells (sarcolemma) ; and the somewhat denser peri- 
mysia and perinenrea which bind muscle cells and nerve fibers 
respectively into bundles, are connective tissues, produced and 
maintained by connective tissue cells which live in between the 
muscle cells and between the nerve cells. 

Epithelial cells compose the epithelia which cover the skin, and 
line the various passages of the body. The function of these cells 
is, in general, protective. Certain epithelial cells, however, have 
become specialized to act as receptors (which will be described 
later), while others have become gland cells. 

Gland cells are found not only collected into glands, but also 
scattered singly in various epithelia. The gland cell has the 
highly developed capacity to manufacture certain substances (such 
as mucus, digestive juices, or epinephrin) which are not needed 
directly by the gland cell, but by the organism at large. 

In certain glands, such as the kidneys, the function is not 
really one of manufacture, but merely of separating from the blood 
certain substances such as urea which the blood brings to them. 
The layers of epithelial cells in those organs act as filters. In 
other glands, such as the liver, pancreas and adrenal glands, the 
process is actually one of manufacture of new substances from 
materials taken from the blood stream. 

Muscle cells are of three kinds: striped muscle (also called 
striated, voluntary and skeletal) ; smooth muscle (involuntary and 
visceral) ; and cardiac muscle. Striped muscle is in general con- 



176 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

nected to the bones ; it is the muscles of the arms, legs, neck, face 
and trunk. Smooth muscle forms part of the walls of the ali- 
mentary canal (gullet, stomach, intestines) : of the blood vessels 
(veins and arteries) ; and of the ducts of various glands, including 
the urinary passages. It is also found in connection with the hair 
follicles, each hair follicle having a muscle attached. Cardiac 
muscle is found only in the heart. It is striped, but non-voluntary, 
and is further distinguished by being a syncytium, in which the 
different muscle cells have anastomosed, or united in such a way 
that they cease to be distinct individuals. This is the only part 
of the body in which cells lose their distinct individuality. 

The function of muscle is to contract and relax. By this simple 
function of shortening and elongating, a vast amount of com- 
plicated work is done. The animal moves its members, moves its 
whole body, breathes, obtains food and drink, chews and swallows, 
digests and excretes waste products, maintains the circulation of 
blood, defends itself from enemies, and effects sexual intercourse, 
through the nicely adjusted contractions and relaxations of its 
myriads of muscle cells. As far as reaction and adjustment to 
environment are concerned, the processes are immediately depend- 
ent upon the muscle and gland cells, which are hence called 
effectors. 

The difference between voluntary and involuntary action need 
not be discussed at this point. While it is in general true that 
skeletal muscle is voluntary in its action, and that smooth muscle 
and cardiac muscle are involuntary, there are numerous excep- 
tions. All striped muscles are capable of involuntary action, as 
well as of voluntary, and they often exhibit finely coordinated 
involuntary action. Certain smooth muscles of the genital system 
(surrounding the urethra of the male and the vagina of the female) 
although characteristically involuntary in their action, may read- 
ily be voluntarily contracted. Certain persons can slow the heart 
beat ''voluntarily,'' and can "voluntarily" secrete tears and 
saliva. 

§3. The neuron. . 

Nerve cells are the essential elements of the brain, spinal cord, 
nerves and ganglia. The typical nerve cell has two or more long 



THE BODILY MECHANISM 177 

fibers of cytoplasm, although some have but one. The cell as a 
whole is called a neuron; the part containing the nucleus, and from 
which the fibers grow, is the cell body. The neuron, or nerve cell, 
is then the cell body plus the fibers. 

Neurons have, so far as is known, but one function, aside from 
that of self -nutrition. This function is variously described as dis- 
charge, production of nerve current, or transmission of irritation. 
The neuron can be stimulated or excited, either by another neuron. 
or by a physical stimulus; and can, upon such stimulation, " dis- 
charge," or so act as to stimulate another cell, which may be 
another neuron, or a muscle or a gland cell. 

If we have a series of neurons, with a fiber of the first in con- 
tact with a fiber of the second; a fiber of the second in contact 
with a fiber of the third, and so on: and if we stimulate the first 
neuron properly, it will stimulate the second, the second will 
stimulate the third, and so on. Obviously, some "process" passes 
through the neuron, passing into the cell body through one fiber, 
and out through another: because a neuron excited at the tip of 
one fiber will excite another neuron with which another of its fibers 
is in contact. This "process" is called "nerve current." Its 
exact nature is unknown, and is the subject of various theories, 
but it is analogous to the burning of the powder in a fuse. Sup- 
pose w^e lay a number of short pieces of fuse end to end, and light 
the free end of the first. The combustion process will run through 
the first piece ? ignite the second, and so on through the whole 
line. Yet nothing travels, except the process of combustion. The 
chief differences between the action of this line of fuses, and the 
action of a chain of neurons are that the neuron has a rapid 
recovery, becoming quickly ready for another discharge ; and that 
the neuron, in many cases, has numerous branches of its fibers in 
contact with many other neurons, and stimulates, at a given dis- 
charge, some of these without stimulating the others. 

The neuron fibers are of two kinds : axons and dendrites. Each 
neuron has an axon ; it may have no dendrites or may have one or 
many. The axon S9 normally conducts nerve current away from 
the cell body, the dendrite towards the cell body. The dendrite 

89Frequently written axone. 



178 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

therefore receives stimulation from another cell: the axon applies 
stimulation to another cell. But the cell Body may receive stimu- 
lation directly from the axon of another cell without employing a 
dendrite. 

The method of connection of nerve cells may be understood 
most easily by considering it from the point of view of the axon. 
Branches of the axon touch other nerve cells functionally in two 
ways: (1) they touch branches of the dendrites of another cell, 
or (2) they touch the cell body of another cell, in the latter case 
usually surrounding the cell body with a network of axon- 
branches. In either case, the point of contact between the axon 
branch and the other cell (body or dendrite) is called a synapse. 
A synapse, then, is the point at which an axon of one neuron 
touches and can stimulate the dendrite or cell body of another 
neuron. 00 The synapse is supposed to be the " valve" which per- 
mits a discharge in but one direction through a neuron. The stim- 
ulation can pass from the axon to dendrite or cell body of the next 
cell: but the synapse will not permit of a back-flow. Hence, in any 
neuron chain in the body, neuron 1 can stimulate neuron 2, and 
neuron 2 can stimulate neuron 3, and so on; but neuron 3 cannot 
stimulate neuron 2, nor can neuron 2 stimulate neuron l. 91 

All neurons may be stimulated "inadequately" by an electric 
current. Certain neurons, however, have apparently developed 
the capacity for being stimulated by certain forces to which other 
nerve cells do not respond. Thus, the rod cells and cone cells in 
the retina of the eye are stimulated by light. The olfactory cells 
are stimulated by odorous gases, and so on. These specialized 
cells are called receptors: and their specialization is the only form 
of differentiation of function in hind, which has been discovered 
among nerve cells. Aside from the receptors, all nerve cells have 



soThe axon may "touch" other cells at many places at which no stimulation occurs; 
just as a well insulated electrical wire may cross or touch many others, but will make 
"electric" contact only at its exposed tip where the insulation has been removed. 

siHence, when the distal part of an axon branch is stimulated inadequately, "cur- 
rent" may flow back in the axon towards the cell-body and out through another 
branch of the same axon, to another neuron (the so-called "axon-reflex") : but not 
through any of the dendrites of the first cell or through its cell-body to axons in 
contact with them. 



THE BODILY MECHANISM 179 

the same function, 92 namely : to be stimulated by a preceding cell, 
and to stimulate in turn a following cell. 

§4. Epithelial receptors. 

Not all receptors are nerve cells. The receptors for taste, the 
receptors for hearing, and the receptors in the vestibule and semi- 
circular canals are modified epithelial cells. Each of these epithe- 
lial receptors is touched synaptically by branches of a dendrite of 
a nerve cell, to which it passes the stimulus. The receptors in 
the three divisions of the inner ear are "hair cells," that is, have 
cilia growing from their free surfaces, and it is apparently by the 
literal "pulling" of these hairs, through the movements of jelly- 
like structures to which the distal ends of the hairs are attached, 
that the stimulation occurs. 

§5. The divisions of the nervous system. 

The terminology of the nervous system is complex and con- 
fusing. Strictly speaking there are two "nervous systems," (1) 
the general system, involving the brain, spinal cord, many gang- 
lia, and the nerves of the soma, viscera and special sense organs; 
and, (2) the local system of the alimentary canal (known as the 
plexus of Meissner and Auerbach) which has a certain relative, not 
absolute, independence of the general system. It is common, how- 
ever, to distinguish (1) the Central Nervous System, including the 
brain, spinal cord and certain ganglia lying close to the cord and 
brain, and (2) the Peripheral Nervous System, including the 
nerves, except those connecting with the viscera and (3) the Auto- 
nomic System, which includes the nerves connecting the cord and 
brain with the viscera, and certain ganglia connected with these 
nerves. Sometimes the "Central Nervous System" is taken as 
including (1) and (2) above. 

Aside from the local alimentary plexus, there is really but one 
"system," with three divisions: afferent, efferent and central. It 
is especially important to remember that the so-called Autonomic 
System (including the Sympathetic System) is not in any wise 



92 A saving clause should be inserted here in regard to the motor cells in the medulla, 
etc., which seem to have the capacity for periodic discharge, independent of stimula- 
tion in the usual sense. In this respect, perhaps, they may be said to have a different 
kind of function from other nerve cells. 



180 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

independent of the " Central System," but bears the same func- 
tional relation to it as does the so-called ' ' Peripheral ' ' System. 

The peripheral and autonomic (visceral) divisions of the nerv- 
ous system are made up of afferent neurons, which conduct nerve 
current towards the brain and spinal cord, and efferent neurons, 
which conduct current- away from the cord and brain. The last 
neuron in any afferent chain or series, either enters the spinal 
cord through a spinal nerve, or enters the brain stem through a 
cranial nerve. Similarly, the efferent neurons leave the spinal 
cord or brain stem through the spinal or cranial nerves. These 
nerves are composed (aside from their connective tissue wrap- 
pings) of axons of efferent neurons and dendrites or axons of affer- 
ent neurons. 93 

The brain stem is composed of the medulla, pons, and thalami, 
with certain attached structures, and is exclusive of the cerebrum 
(cerebral hemispheres) and cerebellum. The brain, therefore, 
may be divided into cerebrum, cerebellum and brain-stem. No 
afferent neurons or efferent neurons connect directly with cere- 
brum or cerebellum: all peripheral and visceral connections are 
with the brain stem or the spinal cord. 

Neurons lying wholly within the brain or the cord, or extend- 
ing from brain to cord, are called central neurons. The central 
neurons are further divided into three classes: the commisural 
neurons, which extend from the right to the left hemispheres of 
the cerebrum, from the right to the left halves of the cerebellum, 
or vice versa; or which connect the two. sides of the spinal cord 
or of the brain stem at the same level: associative neurons which 
connect different parts of the same hemisphere, or the same side 
of the cerebellum, cord, or brain stem: and projection fibers, or 
ascending and descending fibers, which connect cord with brain 
stem, brain stem with cerebrum or cerebellum, and vice versa. 
These are broad distinctions, and many cells in the brain-stem 
obviously are not to be classed in any one of these groups. 

Afferent neurons fall into three general classes. (1) Those 
which are receptors, and whose axons enter the cord or the brain 
stem. Such are the receptors for the dermal, ldnesihejtic, and vis- 

f3 Only in the optic nerve, and the so-called olfactory nerve, are afferent axons present. 
In all other nerves the afferent fibers are dendrites of afferent neurons. 



THE BODILY MECHANISM 181 

ceral senses. These have their cell bodies in the spinal ganglia, 
or in certain equivalent cranial ganglia. Their dendrites extend 
to the structures (skin, muscles, alimentary canal, etc.) whose sen- 
sitivity they serve, and their axons enter the cord or the brain 
stem. The complete afferent pathway in such cases involves but 
a single neuron. If the finger is stimulated, the nerve current pro- 
duced by direct stimulation of a dendrite in the skin is transmitted 
to the spinal cord through a neuron which extends the whole dis- 
tance from skin to cord. The olfactory receptors really belong in 
this first class of afferent neurons, since the olfactory bulb, into 
which the axons of the gustatory receptors extend, is strictly to 
be considered as a part of the brain stem. 

(2) In a second class are those afferent neurons which extend 
between an epithelial receptor and the brain stem. These occur 
in connection with the hair cell receptors for the inner ear, and 
the taste receptors. In these instances, the epithelial cell is first 
stimulated; and in turn it stimulates the afferent neuron, which 
conducts the stimulation to the brain stem. 

(3) In a third class are the afferent neurons of the visual 
sense. In this case, three successive neurons — a receptor and two 
intermediate neurons — are required to transmit the afferent cur- 
rent to the brain stem. Two of these neurons lie wholly within 
the retina. The third sends its axon through the optic nerve to 
the brain stem. This case is peculiar, in that the second and third 
neuron are considered as really belonging to the central, and not 
to the peripheral system. The practical importance for vision of 
the retinal arrangement is not known. All afferent neurons are 
bipolar cells: neurons with one axon and one dendrite. Almost 
all other nerve cells are multipolar, although there are a few uni- 
polar cells. 

In the case of the efferent neurons there are two classes: (1) 
Efferent current is sent to striped muscles through a single neuron, 
whose cell body lies in the spinal cord, or brain stem, and whose 
axon extends to, and has its branch in contact with, the muscle 
cells involved. (2) Efferent current is sent to smooth muscle and 
to gland cells, over relays of two cells. The first neuron has its 
cell body in the brain stem or cord, and its axon extending to a 
ganglion, in which it forms a synaptic connection with a number 



182 



ELEMENTS OF SCIENTIFIC PSYCHOLOGY 



of neurons, the axon of each of which extends to the muscles or 
glands, and ends in contact with the muscle cells or gland cells. 
The latter are the post- ganglionic cells: the former are the pre- 




Sympofhelic Ganglion 



Smooth Muscle 



Fig. 12. — Scheme of reaction pathways commencing in retinal receptors (R), indicating the 
possibilities of connection between these receptors and various effector systems. 

ganglionic cells. Through this arrangement, an axon issuing from 
the brain stem or cord distributes its stimulus to a larger number 
of effectors than would be possible otherwise. The arrangement 



THE BODILY MECHANISM 



183 



is satisfactory for these effectors which may react uniformly in 
groups, but would not be satisfactory for skeletal muscles, where 
nice discriminations in reaction are necessary. 

The functioning of afferent and efferent neurons is relatively 
simple. Current due to stimulation of a given receptor can enter 
the cord or the brain stem at only one point. Current emerging 

Cochlea of Ear ', Ij U 

Lye \ ^ .^^^C 



R 1 Ai > 



Brain Stem 



Skin 



Siriped Muscle fit 





Spinal Cord ', 



Olive Slater 
Fig. 13. — Scheme of reaction pathways terminating in muscles producing finger movement. 



from the cord or brain stem at a given point can go to only one 
effector or effector group. The central neurons, however, pro- 
vide a multiple switching system, by which an afferent route can 
be connected with any one of several efferent routes. If we con- 
sider the cord, brain stem and hemispheres together, they may be 
compared to the exchange of a telephone system, through which 
any calling phone can be connected with any other phone. The 



184 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

difference is that the "sending" (receptors) and "receiving" 
(effectors) stations in the nervous system are distinct; whereas 
they are combined in the telephone system. The nervons system 
is a "one-way system." Brit within this system a given receptor 
can be connected with almost any effector, or with several at the 
same time; and conversely, a given effector may have connected 
to it any one of a wide range of receptors or various combina- 
tions of receptors. 

The multiple possibilities in the way of interconnection of 
receptors and effectors are provided by the many-branched axons 
and dendrites of the central neurons. If we assume that the first 
axon entering a cerebral hemisphere has branches in contact with 
only ten neurons: and that each of these ten have axon branches 
in contact with ten other cells, and so on, a succession of five cells 
between the entry to and the exit from the hemisphere would mean 
a choice of 100,000 routes. No idea of the exact number of pos- 
sibilities can be obtained, but we may be assured that it is so great 
that practically any receptor can transmit current to practically 
any effector. 

The possibilities in the way of switching through the cord and 
brain stem alone are more limited. Only a few efferent routes 
may be connected with any given afferent route, and vice versa. 
As for the functions of the cerebellum, little can be said, although 
we know that it adds greatly to the efficiency of the total switch- 
board system, even if it does not add to its variety. The impor- 
tance of the hemispheres for the mental life is solely in the inter- 
connecting system they provide. 

Sensory and Motor Cortex 

The cortex, or outer part of the cerebrum, in which lie chiefly 
the cerebral neurons, is divided conventionally into sensory and 
motor areas, and the neurons whose cell bodies lie in these areas 
are described as "sensory" and "motor" cells. The ..sensory 
areas are the areas to which the afferent current is sent directly 
from the spinal cord and brain stem, and from which it is directed 
to other parts of the cortex^ The motpr/argas are the areas from 
which current from the cortex is sent to the efferent neurons which 
lead out from the cord or brain stem to the effectors. Current 



THE BODILY MECHANISM 185 

which passes through the cerebrum must enter it at one of the 
sense areas, and leave it again from some point in the motor area. 
Each of the senses is believed to have its particular sensory area 
or "sensory center" in the cortex, and every part of the effector 
system of the body has its definitely localized cortical motor area 
or "motor center." The sensory centers for vision, hearing, 
smell and taste have been located, and the centers for the dermal, 
somatic and visceral senses seem to be identical with, or close to, 
the motor centers for the same parts of the organism. 

§6. Heredity. 

The animal which develops from the original fertilized egg 
possesses characteristics which were largely determined in the egg. 
These characteristics are not merely of structure, but include 
functional tendencies also. The animal will tend to act in ways 
determined by its heredity, and its heredity is all "carried" some- 
how in the fertilized egg. 

It is known that the chromatin in the nucleus is the chief, if 
not the only "carrier" of heredity. Part of the chromatin in the 
fertilized egg came from the female germ cell which produced the 
egg ; the other part came from the male germ cell, when the nucleus 
of the sperm cell penetrated the egg and joined the egg nucleus. 
In the division of the egg into two cells, the combined chromatin, 
which contains the characteristics of the new animal which will 
develop from it, breaks up into chromosomes: and the behavior 
of these chromosomes in mitotic cell division is an intricate and 
fascinating process. 

It will be noticed that we do not say that half of the chromatin 
in the fertilized egg is derived from each parent animal; but we 
say that it is derived from the parent germ cell. This distinc- 
tion is important. Neither the spermatozoon nor the egg cell is 
produced by the organism within which it develops. Take the 
case of the male parent, for example. When his body was devel- 
oped, certain cells, progeny of an original fertilized egg, remained 
in an undifferentiated state, being germ cells, precisely like the 
original egg; while the other cells developed into the body. The 
testicles developed about these germ cells, and they continue liv- 
ing in the testicles, producing other germ cells like themselves and 



186 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

also producing spermatozoa, which are "reduced" germ cells. But 
these germ cells, although living within the body of the animal, 
and deriving nourishment from it, were not 'produced by it, but 
are merely collateral descendants from the same parent-cell. They 
are parasitic on the organism, drawing food from it, and depend- 
ing upon it to introduce the spermatozoa to the vicinity of egg 
cells, that they may fertilize them and so continue the breed of 
germ cells, and incidentally, of animals. Practically, the only 
effect the animal body can have on the normal course of events 
affecting the germ cells living in its own testes or ovaries is to 
starve them, or to refuse to introduce sperm cells to the vicinity 
of eggs, or the converse. The germ cells are descendants of an 
indefinitely long line of germ cells, modified by many cross mat- 
ings of egg with sperm cell; and the bodies in which these germ 
cells have lived, and which have assisted them in their matings, 
have been by-products, which have literally had no progeny. 

It is obvious, therefore, that education or training of the par- 
ents has little or no effect upon the children, but only upon the 
parents; and that improvement in the character of human beings, 
whether physical, mental or moral, is possible mainly through 
selection of the stock having the best heredity, i. e., the germ cells 
which will produce the best human animals. Such improvements 
are passed on to succeeding generations, whereas the improve- 
ments made by education affect primarily only the persons who 
are educated and not their children. 

§7. Reactions and reaction arcs. 

When a sufficient stimulus is applied to a group of receptors, 
we have the process, beginning in the receptors and ending in 
effectors, which we call reaction, Although it is practically impos- 
sible to stimulate a single receptor, we may for the moment con- 
sider the reaction process as it would occur if a single receptor 
were stimulated, and will assume the receptor to be in the retina. 
The receptor (rod cell or cone cell) irritates the next neuron. (small 
bipolar), this in turn irritates the third (large bipolar), through 
the axon of which" a cell body lying in the brain stem is irritated. 
This in turn has an axon extending to the occipital lobe of the 
cerebral cortex, where it irritates a fifth cell, a branch of whose 



THE BODILY MECHA3TCSM 1ST 

axon may extend to the frontal lobe. Froin there, an axon branch 
extends to the motor area of the cortex. There it irritates a 
seventh neuron, whose axon extends downward into the spinal 
cord, where the final neuron, whose axon extends to the muscle 
fiber in the arm. is stimulated, and ends the process by stimulat- 
ing the muscle fibers. 

This whole process is reaction. The contraction of the muscle- 
cells is action. The neural discharge from the receptor to effector 
is the neural transit. 9 * The chain of neurons over which the 
transit takes place is the reaction-pathway or reaction arc. 

"We must understand that no such simple reaction ever occurs. 
Actually, several, or a great many, receptors of the same sense 
are stimulated, and afferent current is sent over a number of par- 
allel routes. Furthermore, the arcs branch in the centers, and 
the resultant reaction involves a great many effectors in various 
parts of the body. Finally, the efferent current directed to a cer- 
tain group of effectors is not derived exclusively from a single 
afferent source, but from a wide range of sources, combined in the 
centers. In the reaction of the finger movement to a retinal stim- 
ulation, for example, the stimulus produces, or helps to produce, 
changes in muscles and glands all over the body: and stimuli to 
receptors in ears. skin, muscles and viscera assist, or modify the 
finger-reaction. 

Yet. since we may consider a single-file reaction arc as a legiti- 
mate representation of a number of parallel routes: and since in 
any given reaction, however complex, there is usually a principal 
afferent branch, and a principal efferent branch, the concept of 
the reaction arc is both permissible and useful. 

All reactions are primarily adjustments of the organism, and 
hence necessarily eventuate in muscular activity, or glandular 
action, or both. Stimuli of various kinds produce reactions which 
provide for the various needs of the animal: reactions of defense. 
of flight, of seeking food. rest, and water, or sexual intercourse. 
All of the activities in which these reactions terminate involve 
glandular secretion as well as muscular contraction. The food 
reaction, for example, involves secretion of the salivary glands. 

94 The terra neural transit is new. arid introduced here "because there is no equivalent 
term in use. 



188 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

and of glands in the stomach, intestines, liver and pancreas. And 
all of these actions are brought about by a wide and complicated 
range of stimuli. The food reaction, for example, is initiated by 
the sight, smell and sonnds of edible objects, and by the internal 
stimulus of hunger. In addition to these primary reaction groups, 
various minor reactions, such as those involved in brushing away 
insects; and multitudes of non-essential reactions, such as those 
of play, develop. 

Eventually, some types of reaction become reduced to the point 
where the actual muscular and glandular activities are slight, and 
perhaps negligible. You hear the chimes ringing the hour; affer- 
ent current is started from the cochlear hair cells, but the efferent 
result is not easily demonstrable. A man walks across the road 
in front of you, and your retinal receptors respond; but no overt 
action on your part follows. In some cases, the reaction is a dif- 
fuse one, affecting slightly the whole organism; in others, there 
is activity of the muscles of speech. Perhaps in all cases of sen- 
sory stimulation there really is complete reaction. It may be that 
in some cases the efferent part of the reaction is short-circuited, 
and the action prevented. But however that may be, these incom- 
plete reactions are of the very highest importance for our mental 
lives, as will be shown later. For the present, we shall deal with 
reactions which are complete, eventuating in demonstrable activi- 
ties. The incomplete reactions follow the same general laws as 
the complete reactions. 

The reactions of which a human being is capable are of almost 
infinite variety. Considering the muscular reactions alone, we 
find that thousands of muscle fibers participate in the simplest 
movements of the fingers. These fibers contract and relax in a 
definite time order, and a change in this time-order, or a change 
in the particular fibers contracting, makes the reaction a differ- 
ent one. The ultimate effects of slight variations in reactions may 
be great. In writing, for example, a vast number of different 
finger and hand movements are possible, and the significance of 
writing e instead of i — a very slight change in the action pattern 
— may be enormous. 

The specific muscle fibers involved in a reaction, and their 
specific time order of contraction and relaxation may be desig- 



THE BODILY MECHANISM 189 

nated the action pattern. The action pattern in any reaction will 
depend npon the specific neural discharges to the muscle fibers, 
and the time order of these; and so we may speak also of the 
neural pattern of a reaction. The neural pattern, in turn, depends 
in part upon the general synaptic conditions in the brain and 
spinal cord, as will be described under the topic of habit forma- 
tion : and in a given synaptic condition, it depends upon the stimu- 
lation pattern, or stimulus pattern applied to the receptors. 

We must take the stimulus pattern into account at this point, 
because reactions do not occur merely to the application of energy, 
where none was previously applied; but may be brought about 
also by the removal of stimulation, or by change in the total stimu- 
lation applied at any time. In short, the stimulus pattern is the 
important factor at all times, so far as the initiation of reaction 
is concerned. 

For example: you are watching a gray spot dimly visible 
through the underbrush; it moves, and you raise your gun; it is 
game, and not a stump. The slight movement made no significant 
increase in stimulus to the eye, but the pattern changed : the dis- 
tribution of stimuli on the retina changed, and a definite reaction 
resulted. Strictly speaking, there was reaction going on all the 
time, but as the stimulus pattern changed, the whole reaction pat- 
tern (neural and muscular-glandular patterns) changed suddenly. 

The vital significance of the reaction pattern will become 
apparent when we have discussed the integrative action of the 
nervous system. 

§8. Types of reaction. 

The five important types of human reaction are: (1) Keflexes, 
(2) Perceptual reactions, (3) Ideational reactions, (4) Volitional 
reactions, (5) Automatic reactions. Keactions of the first class 
are unconscious: those of the second, third and fourth classes are 
conscious: those of the fifth class are less conscious, approaching 
the unconscious type ; and perhaps actually unconscious in extreme 
cases. 

(1) Reflexes, sometimes called "physiological reflexes," are 
reactions such as the "wink" of the eyelids which follows the 
entrance of a grain of sand into the eye, or follows the sudden 



190 ELEMENTS OE SCIENTIFIC PSYCHOLOGY 

approach of an object to the eye; the "knee jerk" which follows 
a stroke on the patellar tendon just below the knee cap; the nar- 
rowing of the pupil of the eye (pupillary reflex) when a strong 
light is flashed into the eye; and the general "start" of the whole 
body when sudden and unexpected noise occurs. 

These reflexes have two characteristics which are important. 
First, they are brief in duration, consisting in general of a single 
contraction or relaxation of a muscle or of the members of a group 
of muscles. Second, they are relatively invariable, a particular 
stimulus always, in the normal subject, producing the particular 
reaction. If the reaction (such as the knee jerk or the pupillary 
reflex) does not follow the appropriate stimulus (the blow on the 
tendon or the flash of light), this failure is evidence of an abnor- 
mal condition of the patient. In many cases the invariability 
extends to the stimulus, one specific stimulus, and one only being 
capable of producing the reflex. 

Reflexes of smooth muscles and glands also occur. The saliva 
starts to flow when the odor of lemon juice assails the nostrils. 
The muscles attached to the hair bulbs contract under the stimulus 
of cold, producing "goose flesh;" the muscular coats of the blood 
vessels contract or dilate under various stimuli, this action in the 
vessels of the skin being apparent as "paling" and "blushing." 
Probably all of the glands of the body are subject to reflex action 
of this kind. 

These reflexes take place probably through the cord or the 
brain stem alone. The afferent current, in the case of the knee 
jerk, is conveyed by the afferent neurons to the cord through the 
third and fourth lumbar roots; is transferred across the cord to a 
motor neuron whose cell body lies in the cord ; and over the axon 
of this neuron the motor current runs out to the extensor muscle 
of the thigh. The arc involves certainly not more than four, prob- 
ably three neurons (one afferent, one efferent and one central), 
and possible only two. The pupillary reflex involves an afferent 
current carried to the optic thalamus by a chain of three neurons, 
and from there back to the iris by a single efferent neuron. In 
other cases the reflex arc may enter the brain stem and from there 
run out through the cord, or vice versa; but it is possible also 
that all such reactions belong in the next higher group. 



THE BODILY MECHANISM 



191 



Vocal Or6ans 



Arm Muscl 



Tendon Spindle 



Recepfors in Skin 




Spinal Ganglion 



Muscle Spindle 



Fig. 14. — Scheme of pathways involved in the knee-jerk, and in the accompanying per- 
ceptual reactions. 1 is the arc over which the reflex occurs : 2 is an arc over which occurs 
the reaction of perceiving the movement: 3 is an arc over which may occur the reaction of 
perceiving the blow (stimulus). 



192 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

In the reflex, no consciousness is involved in the essential 
transit. It is true that in the case of the knee jerk, the patient 
is usually aware of the blow on the tendon, and of the resultant 
"kick," but these awarenesses are not essentially connected with 
the transit which actually terminates in the action. These per- 
ceptions are due to transits over other arcs passing through the 
cerebral hemispheres, and the kick occurs just as perfectly if these 
transits and their associated consciousnesses are absent. In lower 
animals, as for example in the cat, the knee jerk persists after 
the spinal cord has been severed in the cervical region; in man, 
severing the cord in this region temporarily abolishes the knee 
jerk by destroying the tonicity of the muscles; but in every case 
it destroys consciousness both of any stimulation of the leg, and 
consciousness of movement of the leg: and in many cases, the 
knee jerk will in time be restored, without consciousness. 

(2) Peceptual reactions. There is a large class of reactions 
differing from the above described reflexes in that perceptual con- 
sciousness, the perception of some object, is essentially bound up 
with the reaction, forming an integral part of the total process. 
In this class are such reactions as the catching of a ball, pouring 
water into a glass, taking the change the conductor hands you, 
picking up a card from the table, and an endless number of 
similar performances concerning which it is sometimes wrongly 
supposed that the action follows the perception of the object, but 
in which, as a matter of fact, the perception is dependent on the 
reaction rather than vice versa. 

Certain of these reactions, originally perceptual, may in the 
course of time come to be done without the perceptual factor (see 
below), and in general, the vividness of perceptual consciousness 
involved in these reactions varies from high attention to very 
low vividness. The reduction of actions from the conscious level 
to, or towards, the non-conscious level, is a normal and essential 
feature of increasing efficiency of conduct, and is one of the defi- 
nite purposes of education. 

Among perceptual reactions are some that we. call imitative, 
in which the consciousness involved is the perception of an action 
performed by some one else ; and the reaction with which the per- 
ception is united, is the production of the same, or somewhat the 



THE BODILY MECHANISM 193 

same, action by the reacting individual. These are imitative 
reactions in the strict sense; but the term imitation has been 
extended far beyond the field of perceptual reactions, and is fre- 
quently applied to complex processes involving ideation as well 
as perception. 

(3) Ideational reactions. In some cases a reaction, whether 
or not accompanied by perceptual consciousness, involves think- 
ing. I turn around to look at the clock as I remember an engage- 
ment. I open the book on my desk when I think there is a para- 
graph in it I wish to read. I get up and walk into the next room 
when I recall that I left the light burning there. In these cases, 
the thought (imagining, remembering, etc.) seems essentially 
involved with the reactions. 

Under the head of ideational reaction comes the so-called 
"influence of suggestion," where, under hypnosis or in normal con- 
ditions, actions are "suggested" to the reactor by another indi- 
vidual. In these cases, as in all ideational reaction, the action 
does not follow the idea: but the two occur together, as parts of 
a total process. 

The idea with which the action is functionally connected — with 
which it makes up a total psychobiological process — may be the 
idea of the action itself. But such is not necessarily the case. My 
idea, in the process of striking a nail with a hammer, may be the 
idea of striking; but more often it is the idea of the nail going 
into the wood. In stretching out my hand to the table, my idea 
may be the idea of stretching out my hand; but it is more often 
the idea of something on the table. Apparently one and the same 
reaction may at different times be bound up with different ideas; 
but this appearance is probably fallacious. The reactions may be 
alike in their more obvious results, but nevertheless differ in their 
details. It must be noted, moreover, that the movements of the 
limbs and trunk muscles are not the whole action, either in the 
perceptual or the ideational cases ; but that the whole organism is 
apt to be affected. 

In the repetition of ideational reactions, perhaps more emphati- 
cally than in the case of perceptual, the tendency for a primarily 
conscious reaction to become non-conscious, or nearly so, is in evi- 
dence. I push the switch button when the daylight grows dim, 



194 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

not with the thought of the light I am to have, but because I have 
formed the habit of pushing it when the room becomes obscure. 
The thought-element in this reaction, which was present in the 
formation of the habit, has disappeared, leaving the reaction, in 
so far as the consciousness is concerned, on the perceptual level. 
In other cases, which cannot be taken into consideration until we 
have discussed the association of ideas, the conscious element 
seems to evaporate entirely from the reaction, and this is in gen- 
eral a very useful tendency. 

(4) Volitional reactions. In many cases, the ideational reaction 
involves the consciousness of desire, 95 assent or selection, which 
gives it the character we designate as volitional or voluntary, the 
character of will. There is in these cases an anticipatory idea; 
an idea of something which at the time is not in existence; and 
there is the desire of its realization. The desire involved in voli- 
tional reaction may be the desire of the act in which the reaction 
terminates; or it may be desire of some object which the act 
secures; or of some situation which the act brings about. I may, 
for example, will to clench my fist, or will to open my mouth; or 
I may will that the curtain be raised, or that the lamp be brought 
nearer to me. 

Although desire is the characteristic feature of will, there may 
be desire without will, but there is no sharp dividing line between 
the two cases. In many cases, the desire for a certain condition 
is united with an act which is directly relevant to the bringing 
about of that condition. My desire for cooling off, for example, 
may occur with the act of getting out of my chair to go outside, 
the desire and the act forming then a single voluntary reaction. 
My desire to avoid meeting a disagreeable person may be united 
with the action of turning to go down another street. 

In other cases, the desire occurs some time before the prac- 
tically important act. For example, I desire a drink of water, and 
decide to obtain it after finishing this page. There the primary 



95 Aversion may take the place of desire in an aet of will: "aversion either to an 
object or to a situation. It is to be understood that in the general statements con- 
cerning will, aversion 'is to be substituted for desire to make the statement valid 
for the alternative cases. One may act on a desire for the result, or on an aversion 
to the situation which would result from not acting: for instance: one may search 
for water with a desire for the liquid, or a desire to drink; or with an aversion to 
thirst, or an aversion to being unprovided with water. 



THE BODILY MECHANISM 195 

desire, as it first occurs, is not a part of the total reaction which 
includes starting for the drink, although some consciousness is 
involved in that reaction; and the desire may, in fact, recnr as a 
part of it. A new factor, decision, is also introduced in these 
cases. 

As a matter of fact, the first desire in such cases is united 
with an action — is a part of a reaction which has a definite causal 
relation to the later action in which the volition is "completed," 
and the occurrence of this first reaction is the decision. Decision, 
then, marks the completion of the real volition, and the final 
action is either a mere ideational or perceptual reaction depend- 
ent upon the preceding volition, or else, if the desire recurs with 
this final action, it is a new volition resulting from the first. 

The first volitional act, in the case we have just been consider- 
ing, where the completion of the volition is delayed, is an act of 
some kind which will bring about the final act through the proc- 
ess of association (which is to be considered later), without 
necessitating the further operation of desire. This decision may 
not be attained in the first reaction in which the desire occurs, 
but may be the result of a series of ideas (that is to say, as we 
shall show later, a series of ideational reactions), through which 
the desire persists. This is the process of deliberation, in the 
course of which there is usually the occurrence of conflicting 
desires, i. e, desires of conditions whose realizations would be con- 
flicting. 

Deliberation may occur in cases where there is not decision; 
where therefore the act in the final volitional reaction is an act 
directly related to the bringing about of the desired condition. 
For example, I may deliberate whether or not I shall post a letter 
I have written, which commits me to an important step, while I 
hold the letter in my hand; then, I may drop it in the box with 
conscious desire to do so (or with desire to commit myself to 
the course). In such a case, there is no decision; no settling of 
what is to be done before it is done: what is to be done is settled 
in the doing of it. On the other hand, the deliberation might be 
finished, the decision made (to post or not to post the letter), 
before I come to the post box, and no outward alteration of my 



196 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

conduct effected until the moment when I have either to pass on 
or turn towards the box. 

The consciousness of the desire in volition varies in degree. 
The intensity of the desire present also varies, doubtless in a con- 
tinuous way, down to the zero point; so that there is no sharp 
line of division between the mere ideational reaction and the vol- 
untary reaction. The whole matter of the causal efficiency of 
desire is obscure, and we can by no means be certain that an 
increased degree of consciousness of a desire increases the prob- 
ability that it will eventuate in a will-act, or that the reverse is 
true. Desires, we must remember, are actually bodily conditions, 
and must influence our actions whether we are conscious of them 
or not. How their influence is modified by their coming into con- 
sciousness, we cannot say. 

Consent and assent are very probably weaker forms of desire, 
but our present knowledge of the details of conative content and 
conation does not permit us to form a conclusion on this matter. 

(5) Automatic reactions. There is a tendency to eliminate 
the distinctly volitional factor in reactions several times repeated ; 
an elimination which, if it were not further modified, would reduce 
the reactions from the volitional to the ideational type. There is, 
however, the tendency which we have indicated earlier, to reduce 
the ideational reactions to the perceptual level, or to the uncon- 
scious level, by the elimination of the idea from reactions which 
were in their earlier occurrences vividly conscious. The reactions 
involved in rendering a written score on the piano are at first 
voluntary; then, as proficiency increases, they become largely per- 
ceptual. The successive movements in buttoning up a garment 
are probably for a child not merely ideational, but volitional ; but 
for us adults the volitional characteristic is almost always absent, 
and the ideational factor is reduced to a preliminary idea of the 
process as a whole, — if any idea at all is left. The perceptual char- 
acter of the several steps in the series may remain, but frequently 
the whole process will be carried through with only occasional 
perceptions of the details involved. 

The elimination of consciousness from reactions which were 
originally perceptual may be strikingly illustrated from the vari- 
ous reactions involved in a series of regularly repeated movements, 






THE BODILY MECHANISM 197 

such as the waltz. For the learner, the taking of the successive 
waltz positions is vividly conscious: the completion of one move- 
ment of the legs is the consciously perceived stimulation for the 
reaction which brings the legs into the next position. With prac- 
tice this consciousness disappears, and the leg movements follow 
each other like simple reflexes, consciousness being free to take 
account of the general direction of the progress down the room, 
the avoidance of obstacles, and the various contents due to the 
partner. 

These reduced reactions, which were originally highly con- 
scious, and from which the conscious factor has been eliminated 
to a large extent, are called automatic reactions. The class of 
automatic reactions is, however, a large and varied one, ranging 
from the type in which ideational reactions have been reduced 
to the perceptual level with only occasional ideational movements, 
down to the type from which all consciousness, ideational and per- 
ceptual, has been eliminated completely — a type seldom realized. 
Although in the general manner of its occurrence this extreme 
or "pure" automatic action somewhat resembles reflex action, it is 
not to be confused with the latter. That the neural conditions of 
"pure" automatic action are different from those of reflex action 
is indicated clearly by the fact that the former may revert at 
any moment to the conscious type. 

Consciousness is important for the learning process: that is 
to say, for the modification of reactions, or the prevention of 
modification in reactions which have not yet become fixed; but 
the very purpose of the learning process is to automatize, and 
make mechanical, the reactions which have reached a satisfactory 
stage of development, and by the elimination of consciousness, or 
its reduction to a minimal level, prevent further modification of 
these reactions. It is desirable to automatize as much of our reac- 
tivity as possible, leaving the conscious field free to accommodate 
the reactions which must be modified, and to direct in a general 
way the series of automatic reactions, starting, stopping, or modi- 
fying these series as circumstances demand. In general, it is 
better to automatize too much than too little: the individual who 
makes the details of petty and familiar action a matter for need- 
less attention is both emotionally psychopathic and practically 
inefficient. 



198 ELEMENTS OE SCIENTIFIC PSYCHOLOGY 

§9. Local and spontaneous activities. 

Analytically we may distinguish from the true reactions 
initiated by stimulation of receptors, two other forms of activity, 
in one of which, spontaneous activity, receptors are not involved, 
and in the second of which, local activity, no neural action is 
involved. Actually, these two types of activity seldom occur 
unmodified in the human organism; the tendencies to produce 
them being so modified by concurrent reaction tendencies that the 
result is a combination ranging from local activity modified by 
reaction to reaction modified by local activity. 

Local activities are actions of muscle and gland cells not depend- 
ent on stimulation of these cells by neurons, but brought about 
by chemical processes in the effectors themselves. The beating 
of the heart (rhythmic contraction of heart muscle) and the secre- 
tion of urine by the kidneys are types of local activities. 
Although these are normally modified by neural discharge, they 
can go on when the nerve connections with these organs are com- 
pletely severed. As these processes normally occur, therefore, 
they are to be considered as local activities "controlled" (i. e., 
accelerated or retarded) by neural transits. Local activity seems 
to be a property of smooth muscle, cardiac muscle and gland cells, 
not of striped muscles in their normal condition. 

Spontaneous activities are activities of effectors stimulated by 
efferent discharges originating in motor nerve cells, without the 
stimulation of these nerve cells by other nerve cells. The breath- 
ing process is perhaps a type of this spontaneous activity, or 
would be, if we could prevent reaction processes from modifying 
it, as they constantly do. Motor cells in the medulla, it is believed, 
tend to discharge rhythmically to the breathing muscles, produc- 
ing respiration at a fixed mechanical rate. Such breathing would, 
of course, be inefficient, since the rate of breathing must respond 
to the oxygen needs of the body, and although based upon a 
spontaneous tendency, respiration, under normal conditions, is 
largely controlled by reactions. 

§10. Mixed reactions. 

We have seen that pure local activity of muscles and glands 
does not occur in normal life. If the control by the nervous sys- 



THE BODILY MECHANISM 199 

tern were removed, certain muscles and glands might show purely 
local activity, for a time, if other circumstances were favorable. 
The same general considerations apply also to reflex activity. 
There is much more reflex action in the behavior of man and the 
higher vertebrates than appears to casual study. If the cerebral 
hemispheres are removed, and the perceptual components of these 
reflexes removed, they can be evoked as pure reflexes, occurring 
in a machine-like way. The alternate movements of the legs, in 
walking, are partly reflex, partly perceptual: that is, in the com- 
plex arc involved in one of the leg movements, one set of neural 
pathways leads through the cord and brain stem alone, and 
another set leads through the cerebrum as well as through the 
lower structures. Through this branch of the total arc, the 
reaction is subject to integration with, and hence control by, the 
general bodily reactions. Local stimulation of the foot will not 
produce a walking movement, unless proper stimuli have been 
applied to other sense organs, as in seeing the ground: or else the 
idea of walking is present. If, however, the loop in the route, 
which passes through the cerebrum, is removed, the more direct 
connections through the cord and brain stem function with- 
out interference, and by stimulating the bottom of the foot in 
a way similar to that in which pressure on the ground affects it, 
the ivalMncj reflex can be obtained, regardless of general condi- 
tions of stimulation. 

§11. Reactions of the glands and smooth muscles. 

All glands, including the ductless or " endocrine " glands (such 
as the thyroid, adrenal, and pituitary) as well as the duct glands 
(salivary glands, sweat glands, liver, kidneys, etc.) are supplied 
with efferent nerve fibers through the "autonomic" division of 
the nervous system. Some of these fibers end in contact with the 
secreting cells of the glands. Others end on the smooth muscle 
fibers of the blood vessels of the glands. In the case of a duct- 
gland, the ducts, through which the secretion of the gland is dis- 
charged, have layers of muscular fibers, which are supplied with 
efferent nerve fibers. 

The effects of nerve currents on the gland as a whole are 
therefore of three sorts: 



200 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

1. The secreting cells may be directly stirred to greater activ- 
ity, or their activity may be inhibited. 

2. The blood vessels in the gland may be dilated or con- 
stricted, thns facilitating or hindering the activity of the secret- 
ing cells by increasing or decreasing the supply of materials from 
which the cells manufacture the secretions. 

3. The duct of a duct gland may be dilated or constricted. 
By dilation, secretion may be allowed to accumulate in the duct, 
and later squeezed out by contraction. 

If a cut lemon is brought under your nose, there will probably 
be an immediate increase in saliva in the mouth due to the con- 
traction of the salivary ducts, and a further increase due to the 
stimulation of the gland cells, and the increased blood supply due 
to dilation of the capillaries. The same effects may be due to 
the mere sight of a lemon, and will almost always be produced 
by the sight of some one sucking a lemon. Thought of a lemon, 
if the content includes either the taste or the smell of the juice, 
will produce the same result: you may notice a salivary flow as 
a result of reading the above statements. The thyroid gland 
shows in a striking way the increased blood supply due to cer- 
tain forms of stimulation (as in fear and rage), sometimes by its 
visible swelling, sometimes by the "choking" feeling of its pres- 
sure on the wind-pipe. 

All reactions whatever probably involve some glandular effects. 
By use of the so-called " psychogalvanometer ' ' it is easy to demon- 
strate that various perceptual and ideational processes, especially 
those which are emotional, involve changes in the secretions of 
the sweat-glands. 

Activities of smooth muscle elsewhere than in the glands are 
easily noticed. "Goose flesh" is due to the contraction of the 
levator es papilli muscles which pull outwards the hair follicles. 
The smooth muscular coats of the arteries everywhere are con- 
stantly being contracted or relaxed, modifying the blood supply 
of the various organs. These vascular changes may be demon- 
strated by blood-pressure measurements and are seen as blushing 
and blanching of the skin under various conditions of thought and 
perception. 

The muscles and glands of the alimentary and urinary systems 



THE BODILY MECHANISM 201 

although controlled largely by the local nervous system, are played 
upon by all the variations in activity of the central nervous sys- 
tem. The effects of the appearance, smell and taste of food, and 
the effects of worry and happiness, upon the digestive processes, 
are well known. Fear may involve increased secretion of fluid 
in the large intestine, with relaxation of the anal sphincter. Pro- 
longed mental labor may induce constipation. Sudden laughter in 
the female sometimes is accompanied by relaxation of the sphincter 
of the bladder. The heart muscles, although contracting auto- 
matically, are continually stimulated and inhibited by efferent 
nervous currents, which are dependent upon the total integration 
of the afferent currents from various parts of the organism, so 
that the heart action responds to the needs of the whole body. 
Extreme instances of this nervous control are often noticed in the 
sudden quickening or checking of the heart beat, not only con- 
sequent on sensory stimulations under certain conditions, but also 
as an end-result of certain ideational cases. The sudden anticipa- 
tion of a pleasurable occurrence, usually quickens the heart beat, 
and the sudden thought of danger to yourself or others usually 
involves checking, at least momentarily, of the heart action. 

The mechanism of sexual excitement is one of the most com- 
plicated of the bodily systems. Glandular secretion and vascular 
dilation are produced by efferent current from the central nervous 
system, along with contributory activities of striped muscles as 
parts of combined perceptual and ideational reflexes. These effects 
are not merely local, but involve the glands and muscles of the 
entire organism in definite and recognizable ways. The results 
of the general excitement stimulate the purely mechanical reflex 
in which it normally terminates. The reflex may, under some cir- 
cumstances, occur with little effect upon the organism in general: 
but the excitement of sex interest, even in the common social ways, 
is never without local effects. 

It is because of the profound and general effect of sexual per- 
ceptions and ideas that the lavish stimulation due to the theater, 
movies, erotic stories and more direct circumstances which form 
so large a part of civilized social life, is unwholesome. Dancing, 
which has been under the ban at times on account of its supposed 
erotic effects, does not increase these effects on the whole, but 
rather dissipates them. 



CHAPTER X 

EEACTION AND CONSCIOUSNESS 

§1. Degrees of consciousness. 

One of the striking things about consciousness is that it may 
vary in degree : I may be more or less conscious of any given con- 
tent, without any change in the content itself. As I sit here at 
the present moment, I am conscious of the whirring of the elec- 
tric fan in the next room. This whir is a constant sound, which 
affects my auditory receptors continuously. Its intensity, pitch 
and timber do not change to an appreciable extent. Yet, at one 
moment, I am "vividly" conscious of it: or I might say, it is a 
"vivid" sound. At another moment, I am conscious of it much 
less vividly: it becomes a part of the "background" of content. 
Yet the stimulation of my auditory receptors is the same at both 
moments. 

Another way of expressing these facts is to say that I am more 
attentive to the noise at one moment than at another. Attention 
and consciousness, in fact, are terms which are to a large extent 
synonymous: attention is, however, used most generally to desig- 
nate the higher degrees of consciousness. When I am "attentive" 
to any content, I am highly (in degree) conscious of that con- 
tent. When I say that I am "inattentive," I mean that the degree 
of consciousness is low. We speak of attentive consciousness as 
vivid consciousness; and we say also that the content is vivid, 
meaning that we are vividly conscious of it. 

Although we cannot say strictly that consciousness is com- 
plex, or composite (although its conditions are highly complex), 
yet we do find that at a given moment we are vividly conscious 
of one detail of content, and less vividly conscious of other details. 
I may be conscious of the noise of the fan, and of some one's 
voice, at the same time; vividly conscious of one, and much less 
vividly conscious of the other. I may be conscious of auditory, 
visual and olfactory objects at the same time that I am conscious 

202 



REACTION AND CONSCIOUSNESS 203 

of my body, viscerally and kinesthetically, and the different fac- 
tors in the total content may have different degrees of vividness. 
In such a case, the details of content which are most vivid are 
said to be " focal," or "at the focus of consciousness,'' while the 
least vivid are said to be in the margin of consciousness, or 
"marginal." 

It is seldom that the same content, or detail of content, remains 
"focal" for long. The "focus" is constantly shifting, attention 
being now to this detail, now to that. Even in cases of continuous 
attention to one object, the attention is apparently in a series of 
pulses, each of brief duration. Apparently each "act" of con- 
sciousness is a matter of a few seconds, and attention to a single 
object must be repeated, if it is to be continued. Attention to a 
series of objects is, therefore, easier than attention to a single 
object, if it is to be long continued. The duration of attention, 
in any single act of consciousness, is, under usual conditions, less 
than a second, but may be extended to several seconds. 

The question is frequently raised as to the scope of attention: 
as to how many things can be "attended to" at one and the same 
time. Attempts have been made to settle this question by deter- 
mining how many separate objects (words, letters, pictures, etc.), 
presented to vision simultaneously for a fraction of a second, can 
be remembered immediately afterwards. Of such objects, six may 
be remembered by the average person, when the exposure has been 
just long enough for clear vision, and the objects are all familiar, 
and are presented to central vision. Some individuals can note 
and remember but three; others may remember more than six. 
If the objects are related to each other in definitely perceptible 
ways, still more can be remembered. Any number of details so 
related as to form a composite whole may be remembered as a 
single object. 

§2. Integration. 

Consciousness is integrative : that is, it tends, in any act of 
being conscious, to be awareness of total situations, rather than 
of unrelated details. A certain presentation of various forms and 
colors is seen as a single landscape ; a certain varied collection of 
sounds is heard as an orchestral strain; several persons are per- 



204 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

ceived as a group. Several sounds in brief succession are usually 
perceived as more than a series: they may constitute a rhythmic 
group, or a musical phrase. The uniform tendency of both per- 
ception and thought is towards unitary awareness of a complex 
object. This synthetic, or integrative aspect of consciousness is 
of far-reaching importance. When we have integrated objects in 
this way, they acquire definite relationships which determine our 
future thought and future perception. This characteristic of con- 
sciousness has its foundation in the integrative action of the nerv- 
ous system, and is the key to the relation between nerve action 
and consciousness. 

The integrative aspect of neural function is the tendency of 
the various reaction arcs passing through the nervous system at 
a given moment to be welded into a single complex arc, with many 
afferent and many efferent branches. Because of the multiple 
synapses of neurons in the brain, there are routes through which 
any arc may establish connections with any other arc; and the 
fundamental tendency of the nervous system is to establish such 
connections. In other words, aside from certain limited reflexes, 
the nervous system tends to act as a whole : to integrate. 

The player catching a ball, for example, reacts principally by 
arm and head movements, to a visual stimulus. But he reacts 
also with the muscles of the trunk and legs, all of which are 
brought into play. In addition, the smooth muscles of the arteries, 
and even of the alimentary canal, are affected, and changes in 
the tensions of these muscles may be demonstrated in many cases. 
It is probable that the glands throughout the organism: digestive, 
urinary, sudorific and ductless: are involved, although the gland- 
ular part of the reaction may not be important in this particular 
case. All these details in the total reaction are not results of the 
single stimulus of the approaching ball. ' Other visual stimuli, 
such as those of the runner between bases, and the basemen, are 
highly important. The player will not catch in practice in exactly 
the same way as in a close game. The auditory stimuli; the yells 
of the other players, and of the crowd: are stimuli which may 
materially alter the reaction. All these stimuli contribute to a 
single reaction, involving practically the entire organism, the vari- 
ous component transits of the reaction being integrated in the 



REACTION AND CONSCIOUSNESS 205 

brain and brain stem. In this total reaction, however, there is 
one dominant transit; namely, the transit from retinal receptors 
to arm muscles ; and although the player is really conscious of the 
various visual and auditory contents mentioned above, and of 
many other objects, including his own body, the ball is at the focus 
of consciousness. The player is, for the moment, attentive to, or 
principally conscious of, the ball. The next moment, his attention 
may be turned to the runner, or to a baseman; but this requires 
a second reaction, following the first one. Perceptual attention, 
then, or a high degree of perceptual consciousness of a given 
object, depends upon an integration of the nervous system, in 
which the arc initiated by the stimulus corresponding to the object 
is dominant. From this point, the step to the discovery of the 
physiological conditions of consciousness is not far. 

We have explained that three types of reaction (perceptual, 
ideational and volitional) are "conscious," that is, they involve 
perception or thought as a part of the total process included 
between the stimulation of the receptors, and the muscular or 
glandular activities. The other two types of reaction: simple reflex 
and pure automatic reaction, seem to involve no consciousness, 
although other conscious reactions may accompany them. We 
must now compare these reaction types more closely, in order to 
discover, if possible, the reasons for the appearance of conscious- 
ness in the perceptual, ideational and volitional forms, and its non- 
appearance in the simple reflex and pure automatic forms. 

Actions of the simple reflex type, as we have already pointed 
out, are due to neural transits involving the spinal cord or the 
brain-stem, or both, but not essentially the cerebral hemispheres, 
and probably not the cerebellum. Conscious reactions, on the 
other hand, do involve the hemispheres, 96 and it seems improbable 



^Because of the fact that conscious reactions involve the cerebrum, there grew up 
the assumption that the cerebral neurons are specifically different in function from the 
neurons in other parts of the body, and that these cerebral neurons, in some specific 
way produce, or condition, consciousness. This assumption has become very thoroughly 
popularized, so that its eradication is a difficult task. Certain psychophysiologists 
have gone further, and adopted the phrenological assumption, that cells in different 
parts of the cerebrum produce different ''kinds" of consciousness: visual conscious- 
ness being attributed to certain groups, auditory consciousness to others, imagina- 
tion and memory- to others, and so on: an obvious confusion of the concept of con- 
sciousness. These assumptions should be abandoned, because there is no evidence 
that different cerebral cells have different kinds of functions, or that the cerebral 



206 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

that a reaction which does not involve the hemispheres, or some 
portion of them, can be conscious. 

The significance of the connection of conscions reactions with 
the cerebral cells lies in the integrative control or dominance 
which these cells may exercise over the whole organism, not 
because of any qualitative peculiarity of these cells, but through 
the multiplicity of interconnections between them. Nerve current 
entering the human cord or brain stem through some afferent 
channel, and reflected outward from thence, without ascending to 
the hemispheres, has a limited range of efferent distribution, and 
its immediate effects upon the organism are consequently local, 
rather than systemic. Afferent current which reaches the cere- 
brum, however, may be reflected outward to any part of the body 
whatsoever, or to several widely different parts of the body, 
because the synaptic connections of the cerebral cells are so com- 
plicated that a circuit is possible from any receiving cell in the 
cerebrum to any of the cells which discharge into the brain stem 
or cord. Moreover, connections may be established in the cere- 
brum between any or all of the afferent-efferent discharges 
through it, so that the results of any afferent current reaching the 
cerebrum may be systemic, that is, may affect practically the whole 
organism. 

The superior integrative control which is exercised through the 
cerebrum, we repeat, is not due to any peculiar sort of process in 
the cerebral cells, but is due to the arrangement of the neurons, 
through which a very complex system of synaptic connections is 
possible. We may compare the centers (cell groups) in the cord 
and brain stem to a series of local switch-boards, which are rela- 
tively independent of each other except in so far as they are con- 
nected through a grand central switch-board — the cerebrum — and 
through a supplementary switch-board — cerebellum. Yet the kind 
of activity which occurs in each switch-board is the same. 

Consciousness, in short, is not the function, or the result of 
the function of specific nerve cells: it is a function of, or dependent 
upon, the systematic activity or cooperation of large groups of 



cells in general have functions different in kind from those of other nerve cells, ex- 
cept in regard to the relative energy of discharge, sensitivity to stimulation, and 
details of synaptic connection with other cells. 



REACTION AND CONSCIOUSNESS 207 

cells, among which are included in many cases muscle and gland 
cells, along with peripheral and central neurons. In other words, 
it is conditioned by the integration of the nervous system. Whether 
in any cases the activity of muscle and gland cells may be com- 
pletely eliminated, without eliminating consciousness, is a topic 
for further investigation and discussion. 

The energy of the reaction which conditions consciousness does 
not seem to vary with the vividness of the consciousness, but the 
degree to which the reaction involves the total organism does vary 
with the vividness. Above the strictly physiological or simple 
reflex, various degrees of integration of the nervous system are 
possible, involving the total effector system in corresponding 
degrees; and in this degree of integration we find the only pos- 
sible physiological concomitant of attention, or the degree of con- 
sciousness. 

The stimulation of the retinal receptors, for example, may set 
up a reaction which is definite and distinctive in that it is the 
response, spontaneous or habitual, of a certain limited part of the 
effector system, which is appropriate to that stimulation. This 
response may be a movement of the arm and hand, as in grasping 
the object, or a movement of the vocal organs, as in speaking the 
name of the object, or some other movement. If this reaction 
is connected with other reactions going on at the same time, 
through the cerebral synapses, consciousness of the object is pres- 
ent. If this cerebral connection is such that the other reactions 
are little modified, the consciousness of that particular object is 
of low vividness. If the connection is such that other reactions 
are modified generally, and in important ways, the consciousness 
is of high vividness: there is a high grade of attention to the 
object corresponding to the stimulation. 97 

Let us return now to the case of the ball player. In catching 
the ball, the reaction is primarily to the ball, but modified essen- 
tially by the stimulation from (among others) the runner. The 



97 Since the situation in regard to the simple reflexes differs only in degree, from the 
reactions with well marked integration, it may be that these simple reflexes through 
the brain-stem and cord are not absolutely unconscious, but merely so low in degree 
that the consciousness is negligible. This is a matter concerning which no decision 
can be made at present. That is to say, we cannot discover at present at what low 
stage of integration consciousness first appears. 



208 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

player's attention is on the ball, and lie is conscious in low degree 
of the runner. Neurally, the current from the visual receptors 
integrates the whole system; the neural path from these receptors 
to the muscles involved in catching is the main route: the cur- 
rent from the receptors stimulated by the runner is integrated 
with the dominant current, and is contributory to its effects. A 
moment later, however, the runner is the object of attention and 
reaction. The current from the visual receptors stimulated by the 
runner becomes the dominant current, and all other afferent cur- 
rents, although integrated with this into the total efferent dis- 
charge, are subsidiary. 

In effect, then, we may say, (1) that the neural condition of 
perceptual consciousness of an object is that the afferent current 
from the receptors stimulated by that object shall be integrated 
with the current coming in from other receptors generally, into 
a systemic discharge, in which the total stimulus pattern is related 
to the total reaction pattern through a unified neural pattern. (2) 
That the condition of focal attention, or maximal degree of con- 
sciousness at any time, is that the neural transit over the arc cor- 
responding to the object shall be the dominant one : all other affer- 
ent currents being merely contributory to, or modifying, its effer- 
ent discharge, and the total efferent discharges being directed 
with reference to the specific discharge of the main route, and in 
furtherance of its results. These conceptions are not based upon 
specific hypotheses as to the physiology of the nervous system, 
for exceedingly little is known of that physiology. The concep- 
tions are simple statements of the facts of animal response to 
stimuli: statements in terms of the known details of behavior of 
neurons. 



CHAPTER XI 
INSTINCT AND HABIT 

§1. General distinctions. 

Whenever receptors are stimulated, reaction occurs. This is 
the general law to which there are no known exceptions in the 
normal waking animal. The reaction is not to a single, isolated 
stimulus, but integratively to the total stimulus pattern of the 
moment, and is modified by preceding stimulations. Reactions at 
any moment may include the inhibition or checking of activities 
already in progress. 

The specific results of stimulation are produced through neural 
transits, which originate in the receptors, enter the spinal cord or 
brain stem, may or may not ascend to the cerebrum, emerge from 
the cord or brain stem, and flow through efferent fibers to muscle 
cells or gland cells, modifying the activities of these cells. In the 
case of a reflex, the current entering over a certain route has a 
fixed route of emergence, so that the same stimulus produces 
always the same, or nearly the same result, regardless of what 
other stimulations may be occurring simultaneously with the 
stimulus of the reflex. In the reflex, the afferent and efferent 
neurons are apparently in permanent synaptic connection, or else 
the afferent neuron is in permanent connection with a central 
neuron, which, in turn, is in permanent connection with the effer- 
ent neuron, so that current sent in over the afferent neuron will be 
discharged outward over the particular efferent neuron, regardless 
of what other currents are flowing through the nervous system. 
In these cases, therefore, a specific stimulus will always pro- 
duce a specific action. The knee jerk, or patellar reflex, is a typi- 
cal simple reaction : a blow on the patellar tendon, in the normal 
animal, will produce a contraction of the extensor muscle of the 
leg, no matter what other stimulations may be acting on the 
animal, although these other stimulations may influence the degree 
of the contraction. 

209 



210 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

Perceptual and ideational reactions are more variable. Whether 
a specific stimulus: for example, the sound of a bell: will produce 
a certain action or not, depends upon the total stimulation pres- 
ent, and upon the predisposition of the central nervous system. 
A great range of alternative routes are open to the afferent cur- 
rent which has entered the cerebrum, because of the multiple 
synaptic contacts of the central neurons, and the variability of 
the connections at these synapses. Whether this or that route 
shall be chosen depends not only upon the other afferent currents 
pouring into the central nervous system, but also on factors which 
cannot be identified as yet, but which can be summed up in the 
vague term predisposition. The sound of the bell may result in 
your immediate rise from your chair: but if some one speaks to 
you at the same moment, the result may be different. The bell at 
ten o'clock may not cause you to rise, although the same sound 
at twelve causes that action. 

Some predispositions to reaction are learned, or acquired by 
practice, that is: they are due, or largely due, to past reactions 
of the same sorts. Reactions in accordance with these predisposi- 
tions are called habits. There are other predispositions which 
are not acquired 98 in this way, but which are due to heredity and 
growth, modified by previous reactions of other sorts only. These 
predispositions are called "innate," and reactions in accordance 
with such non-learned predispositions are called instinctive reac- 
tions. 

§2. Drainage and habit formation. 

In a normal individual, certain definite stimuli will usually pro- 
duce definite reactions. If a word is spoken at your right, you 
turn the head in that direction. If light is flashed in your eye, 
you close the eye, turn the head away, or react in both ways. If 
a certain color is placed before you, you will make the reaction 
of saying "green," or some other vocal reaction. Some of these 



ssThe actual meanings of the terms "acquired" and "innate" are liable to serious 
confusion. Innate predispositions are not necessarily operative at birth: many of 
them appear much later, and some are operative before birth. Predispositions acquired 
by the process of growth, and general reactions, and not dependent on the animal's 
previous reactions of the same type, are not "acquired" in the sense in which the term 
is technically used. Inherent and learned are much better terms. 



INSTINCT AND HABIT 211 

reactions have been learned. Yon react by saying ' 'green" when 
a Frenchman wonld say "vert": and a child who had not been 
tanght the names of colors wonld say neither of these. Other 
definite reactions are instinctive. The child a few honrs old will 
follow a moving light with its eyes, and will begin the sucking 
reaction as soon as its lips touch the nipple. Its nervons system 
is so disposed, through its growth and development, that certain 
stimuli cause definite reactions, through definite neural pathways. 
Yet reactions can be modified, so that a certain stimulus will pro- 
duce a reaction which it formerly would not. This modification 
of reactions may be learning, or habit formation. 

The possibility of habit formation is provided through the 
fundamental integrative tendency of the nervous system, which 
manifests itself in the simpler details of learning in a form to 
which we apply the term drainage: the tendency of a neural 
transit, when definitely established, to divert other transits from 
their normal efferent courses into its efferent channel. This drain- 
age tendency is illustrated in a striking way by experiments which 
have been performed on dogs by Pavloff and his pupils. A normal 
dog, if hungry, shows a definitely increased flow of saliva, when 
he is allowed to smell or see food to which he is accustomed. Obvi- 
ously, there is an effective reaction arc from the olfactory recep- 
tors, through the central nervous system, to the salivary glands; 
and the transit over this arc ends in increasing the activity of 
the gland cells. By means of a surgical operation, Pavloff brought 
the duct of one of the salivary glands of a dog to the outer sur- 
face of the cheek, so that the flow of saliva could be readily noted 
and measured. It was then easy to demonstrate that excitation 
by the smell of food produced salivary flow, but that the ring- 
ing of a bell did not. The dog was then fed regularly for some 
days, a bell being rung each time he was fed. After a certain 
course of this combined stimulation, it was found that merely ring- 
ing the bell would cause a flow of saliva. The simplest conclu- 
sion would be that a new arc had been made effective, from the 
auditory receptors to the salivary glands. The strong discharge 
to the salivary glands, due to the olfactory stimulation, "drained" 
into it the afferent current from the auditory receptors, which 
normally would have gone to effectors other than the salivary 



212 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

glands, and made these glands the terminus of the auditory 
reaction. 

The explanation as given is probably too simple. The audi- 
tory stimulation probably did affect the salivary glands in the 
first place, but not much: the major effects of the stimulation were 
produced on other effectors: muscles which erect the ears, and 
so on: or else diffused to large numbers of effectors with no great 
effect upon each. In either case, the efferent discharge to the 
salivary glands was relatively small. Now, with the strong effer- 
ent discharge to salivary glands over the arc from the olfactory 
receptors, more of the auditory transit is diverted to that par- 
ticular effector group: and this having occurred once, increases 
the tendency for it to occur again, until finally a habit of discharge 
is formed from the particular reaction pattern, due to ringing the 
bell, over the customary afferent route and the newly formed 
efferent route, to the salivary glands. /This habit is the tendency 
for neural transits, resulting from the same, or similar, auditory 
stimulus patterns, to pass, in the future, over the new efferent 
route, even when the olfactory transit, which originally " drained " 
the auditory transit into the efferent part of its arc, does not 
occur. 

The general facts of drainage have long been known: it is not 
a new discovery that stimuli which originally did not produce a 
certain action could be made to do so by a proper course of train- 
ing an animal. It has been known from prehistoric time, for 
example, that animals could learn to come for food when auditory 
stimuli were given, through the giving of these stimuli at times 
when the animals were being fed. It is, moreover, a matter of 
common knowledge that the visual perception of a lemon, espe- 
cially of a cut lemon, will excite salivary flow in persons who have 
sucked lemons, although, of course, it would have no such effect 
on a person unfamiliar with the taste of lemon juice. The value 
of Pavloff's experiment consists in its putting a well-known fact 
in a simple and definite form, so that the mechanism is made 
plain. Salivary secretion following olfactory stimulation is 
usually listed as a reflex, and the most important transits involved 
are through the brain stem alone. Normally, however, the reac- 
tion is perceptual, or, at least, mixed, involving transits through 



INSTINCT AND HABIT 



213 



the cerebrum, with consciousness of "smell of food," or "food." 
It is probable that if these cerebral branches of the total transit 
were excluded, the reaction would persist, in that case becoming 
a pure reflex. In that case, however, the drainage of the audi- 
tory afferent current into the salivary efferent route would not 
occur: the salivary reflex could not be modified. Habit forma- 
tion depends essentially upon synaptic connections established in 
the cerebrum, or cerebellum, or both. Hence, the name "condi- 
tioned reflex which is applied to new reactions, like the auditory- 
salivary, is misleading. 

The modification of the auditory reaction in the dog is a clear 
illustration of the conventional distinction between instinctive 
action and habit. The original salivary reaction is described as 
instinctive : saliva flows at the smell of food, because it is assumed 
the dog's nervous system is by heredity predisposed to shunt the 
current of this particular olfactory origin through to the salivary 
glands. The instinctive auditory reaction, on the other hand, 
includes, among other details, the "pricking up" of the ears. The 
modification of this reaction in such a way as to produce salivary 
activity from auditory stimulus is habit formation, and the reac- 
tion thus established is a habit. 

It is possible, however, that the olfactory-salivary reaction is 
not absolutely instinctive, but is also a habit, developed from the 
instinctive salivary reaction for food in the mouth. The contrast 
betAveen instinctive action and habit has been overemphasized in 
the past. All habits are based upon instinctive action, and in the 
human animal, almost all instinctive action is modified by habit 
formation as soon as it is manifested. There may be a few instinc- 
tive reactions, such as sucking, which are little modified, and per- 
sist for some time in practically the form of their first appearance. 
In the lower animals, instinctive action, relatively little modified 
through life, is more common. But in every animal in which habit 
formation takes place, the modification of instinct is itself an 
instinctive process. The dog, for example, has a nervous system 
so constituted that the salivary reflex will necessarily modify the 
auditory reflex. The habit, therefore, is merely a more compli- 
cated instinctive reaction, or rather, an instinctive reaction 
depending upon a definite sequence of stimuli, rather than upon 



1 



214 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

a momentary stimulus pattern. The dog's nervous system is so 
constituted by heredity that the salivary reaction occurs when a 
certain olfactory stimulus is given. It is also so constituted by 
heredity that the salivary reaction will occur when a certain audi- 
tory stimulus, following a certain number of applications of that 
auditory stimulus together with the olfactory, are given. Are not 
both of these reactions, then equally instinctive! 

The distinction between "habits" and "instinctive reactions" 
is a useful one, if we remember that habits are complicated instinc- 
tive reactions, and that habit, i. e., the tendency of the reaction 
to any stimulus to be repeated when the stimulus recurs, applies 
to instinctive actions as well as to "habits." 

§3. Instinctive reactions and instincts. 

The fact that the reaction to a given stimulus pattern may 
be modified in a great variety of ways, implies that there are, at 
any time, a variety of routes over which the reaction may pass, 
which are equally possible, so far as the particular stimulus 
pattern is concerned; and that other conditions determine which 
of these routes will be followed. Consider, for example, the pres- 
entation of a red rose, visually, to an educated adult. From that 
stimulus pattern (the retinal image of the rose), a number of 
reactions are possible. The hand may be stretched out to grasp 
the rose ; the gesture of refusing the rose may be made ; the word 
' ' rose ' ' may be spoken, or written ; or any one of a great variety 
of reactions may follow this stimulus, according to conditions 
other than those of the rose pattern. What are the conditions 
determining the reaction? 

These conditions include, in part, other stimuli presented 
simultaneously with, or just preceding, the rose-stimulus. If the 
spoken words ' ' don 't touch this ' ' accompany the presentation, the 
reaction will be different from that which results when the words 
"take this" are spoken. If the rose is growing on a bush, along 
with a great many others, the total stimulation may determine a 
reaction different from that occurring when the rose is alone, in a 
vase. The presence of olfactory, tactual or organic stimulation 
may be effective in determining the reaction. 

But over and above the stimulations simultaneously present 



INSTINCT AND HABIT 215 

with, and those just preceding, the visual rose stimnlns, the 
reaction is determined by habit. Other things being equal, the 
reaction which has occurred before will be the reaction of the 
moment.; and the habitual or customary reaction may be the one 
which appears in spite of the fact that the attendant stimuli are 
very different from those which have previously occurred with 
the rose-stimulus. 

The consideration of habit leads us back to the question why 
a certain reaction, now occurring as a habit, occurred in the first 
place. If the reaction occurs now because it occurred previously, 
why did it occur previously? And so we are led back to the prob- 
lem of its first occurrence. And the reason for the first occurrence 
is found in instinct. The nervous system of the individual has 
developed in such a way, under the influence of heredity, that a 
certain stimulus pattern produces a certain reaction. Given this 
start, habit formation is possible. 

Let us consider the reactions of a new-born babe. Normally, 
it cries, as soon as the cold air strikes it, or a brief time there- 
after. If it did not cry, it would strangle. Perhaps the effective 
pattern is the coldness and the incipient asphyxiation, which 
together initiate the reaction which clears the respiratory pass- 
ages of fluids. 

Now this reaction is instinctive, and it is sometimes spoken 
of as an instinct. By 'Ia n instinct " we mean any combination of 
instinctive activities which produce a definite, and on the whole 
useful, result. In this case, the results include the production of 
sound stimuli which call the attention of adults to the presence 
and needs of an infant, and include also the clearing of the 
respiratory passages. The sucking reaction, mentioned in the pre- 
ceding section is another so-called "instinct," whose result is 
the nourishment of the infant. Later, the walking instinct, the 
talking instinct, and a multitude of others, will make their appear- 
ance, and finally, the sexual impulse, whose practical result is the 
fertilization of the female by the male. 

The instincts of the human animal, with the exception of those 
which appear at the time of birth, are incomplete: they require 
habit formation to perfect them, and fix them. In the lower 
animals, the instincts are much more complete, and many of them 



216 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

remain through life practically unmodified by habit formation, 
while others are slightly modified. The first nest built by a bird, 
and the succeeding nests built by the same bird, vary only in 
accordance with the materials available, and with the weather, 
and the presence of enemies. In similar circumstances, the bird 
builds no better, no more efficiently in any way, the second or 
tenth time than the first. The young duckling, which enters the 
water a few hours, or perhaps sooner, after hatching, swims effi- 
ciently, and what improvement occurs is made very quickly. The 
walking of the young quadruped improves, in the main, merely 
by the gaining of muscular strength. 

In the case of insects, there is no chance for improvement of 
their most complicated instincts, because they are active but once. 
This is true of the whole reproductive process of some insects. 
The male copulates with the female but once. The female bee 
may continue to produce eggs for several years, and the workers 
build many combs: but some wasps build but one nest, and the 
females lay but one set of eggs. Certain female wasps build nests 
of mud or paper, catch spiders and other insects which they 
stupefy with their stings, and deposit in the cells in their nests, 
deposit their eggs in proximity to the food so stored for the young, 
seal the cells, and then die before the young emerge. The young, 
upon hatching, go through the same cycles of instinctive activity, 
with no opportunity to perfect the activities by repetition. 

The flying instinct of birds is apparently improved by prac- 
tice, that is to say, habit formation, or learning. There is no 
" teaching " by the parent bird (popular theories to the contrary 
notwithstanding), yet the continued exercise of the crude flying 
instinct perfects and fixes it. The details of this sort of habit 
formation are perhaps more complicated than in the formation of 
the auditory-salivary reaction in the dog, although to an uncritical 
view such "practice" effects may seem much the simpler. 

The hunting and fighting instincts of carnivorous animals also 
seem to be improved by practice, although it is impossible to say 
that this is really so. The improvement in such reactions may be 
really a matter of growth, and normal development of the neuro- 
muscular structure, and practice may have nothing to do with it. 

The human talking instinct is one which shows modification 



INSTINCT AND HABIT 217 

by habit formation in a very high degree. At almost eight months, 
on the average, sometimes earlier and sometimes later, the child 
begins to show a vocal activity quite different from the crying, 
laughing and gurgling characteristic of the younger infant. He 
begins to articulate syllables. He may commence with gutturals, 
such as ' ' ga' ' and ' ' kow : " or with labial s such as ' ' muh " or ' ' pa. " 
Often the infant, left to himself, will repeat a syllable over and 
over to himself. As the instinct develops, he adds other syllables, 
and makes combinations, and later forms sentences. These reac- 
tions are very soon modified through the effects of auditory stimu- 
lation (words spoken by adults or other children) chiefly, but also 
by visual, tactual and food (gustatory and olfactory) stimuli 
applied at critical times. The result is that the child acquires 
language, and the part played by habit formation in this process 
is sufficiently well illustrated by the fact that the child brought 
up among English speaking people speaks English, but if brought 
up among French speaking people speaks French. In fact, there 
is no doubt that children of any European stock, if brought up 
from birth among people speaking any language, civilized or sav- 
age, would learn to speak that language as well, at any age, as a 
person of the same age, of the race to which the language belongs: 
pro\ ided always that the auditory sensitivity and the general 
intelligence are equal in the two cases. 

The list of "instincts" of human beings is large, as the list 
of practical results which are obtainable through instinctive 
activity is large. But since the results obtainable may be con- 
sidered in larger groups, of a systematic sort, the instincts also 
can be grouped into larger instincts. A common grouping, or 
classification, distributes all instincts into two grand instincts: the 
self -preservative and the reproductive; a division based on the 
fact that all results obtained by animal reaction can be considered 
as either contributory to the preservation of the life of the indi- 
vidual, or to the production of new individuals, and hence to the 
preservation of the species. 

Instinctive reactions, in fact, may be grouped under a vary- 
ing number of classes, in accordance with our interests in classi- 
fying, as determined by the various classes of results which may 
be effected in the world. If we are interested in the distinction 



218 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

between the satisfaction of sexual impulses as an end in itself, 
and the propagation and care of progeny as a separate end, we 
divide the ' ' reproductive " instinct into the amatory and the par- 
ental instincts. If we are interested in the combat of men and 
animals, as distinguished from the ends attained by combat, we 
distinguish the "combative" or " righting " instinct. If we are 
interested in the process which brings men together in social 
groups, and animals in herds or swarms, we distinguish the "gre- 
garious" instinct. 

The list of instincts given by McDougall is sufficiently illus- 
trative of the various lists which have been prepared. McDougall 
lists flight, repulsion, curiosity, pugnacity, self-abasement, self-as- 
sertion, parental, reproductive, feeding, gregarious, acquisitive, 
and constructive instincts, with ' ' a number of minor instincts such 
as those that prompt crawling and walking." He assumes, how- 
ever, a further list of "general" tendencies towards sympathy, 
suggestibility, imitation, play, and habit formation. 

The drawing up and discussing of lists of "instincts" is inter- 
esting, and may be useful, if we remember that the classifications 
are: (1) teleological, that is, determined by the ends or results 
of reactions, as these ends are discriminated, not by the animal 
itself, but by the classifier. The "instincts" are not strictly 
psychological nor physiological systems. (2) That the division 
into "instincts" is arbitrary, and that any classification which is 
based on real "ends," and which suits the purposes of our dis- 
cussion, is as legitimate as any other. It is precisely like a filing 
system for documents : the system to be adopted is the one which 
makes reference convenient, and what is convenient for one pur- 
pose may be inconvenient for another. "Instincts" cannot legiti- 
mately be made the basis for "systems" of Social Psychology, or 
for any other theoretical constructions. 

The fact that "instincts" are arbitrary groups, made for the 
logical purposes of the classifier, is made evident from the appear- 
ance of the same reaction in several "instincts" at once. The 
wolf, or the human animal, in pursuing game, may be exhibiting 
the "hunting instinct," the "acquisitive instinct," the "self 
preservative instinct" (since the food derived from the game will 
sustain his life), the "paternal instinct" (since the production 



INSTINCT AND HABIT 219 

and protection of his progeny depend upon the securing of food 
for himself, as well as for them), and even the ''gregarious" and 
4 ' self preservative" instincts. 

Any given instinctive physiological and psychological reaction 
may be, at different times, a part of any of the "instincts" in 
snch a list as McDougall's. Fighting may be combat for life 
itself against an active attack. It may be a struggle for food. It 
may be a struggle for a female (or on the part of a female for 
a male) in pursuance of the instinct of sex gratification. It may 
be combat for a female, but in pursuance of the tendency to beget. 
It may be in defence of progeny. It may be directed to "grega- 
rious" ends, in the case of an animal or a man who is threatened 
with expulsion from, or ostracism in, a herd or social group. 
It may be in performance of an acknowledged leader's command, 
in direct self-abasement towards the leader. Or it may be a means 
of self-assertion. It may be a means toward "acquisition," or a 
form of play. 

So with running, hiding, and practically all the definite com- 
plex reactions of which the animal is capable. The particular 
"instinct" the reaction expresses is in part dependent upon cir- 
cumstances of the actual reaction, but in large part on the whim 
of the one who classifies it. This must always be born in mind 
in considering "instincts." The more useful course is to consider 
instinctive reaction psychologically, that is, as definite reactions 
to definite stimuli; and in connection with the desires and other 
emotional states of the animal which reacts. 

§4. Consciousness and volition in instinctive reactions. 

"Instinct" is frequently contrasted with "intelligence:" but 
such contrasting is misleading. "Intelligence" is a term which 
has many meanings. It is sometimes defined as the "ability to 
profit by experience," or "ability to learn," which means either 
general ability to form habits, or ability to form habits of a use- 
ful kind. Now we haveTseen that the formation of habits depends 
upon an instinctive reaction foundation, and that it is itself an 
instinctive process. There is, therefore, no opposition between 
instinct and intelligence in this definition of the term. 



220 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

The mistake has been made frequently of assuming that man, 
who has more "intelligence" than the lower animals, has less 
"instinct" or fewer "instincts." Such is not the case. The 
human animal is at least as richly endowed with instinctive reac- 
tions as any animal, and the chief difference is in the superior 
modifiability of human instincts. Which means, after all, merely 
that man has a richer instinctive endowment. 

If we stress the modifiability of instinct as the characteristic 
of intelligence, we are not far wrong. But in this case, the dis- 
cussion reduces to the mere application of a terrm which because 
of its other connotations, is a constant danger to clearness of 
thought. 

In a still more vague meaning, the term intelligence is applied 
to the capacity to react efficiently, that is, with advantage to the 
individual, in the circumstances in which the individual is nor- 
mally placed. In this sense, we may discuss the "intelligence" 
of wasps, who act, apparently, through instinctive reactions of 
the extreme unmodifiable sort. In this sense, we apply the term 
to "intelligence tests," and some workers in the field of mental 
tests even speak of measuring ' ' native intelligence, ' ' whatever that 
may be. A strong case may be made out for the claim that "intel- 
ligence tests," in so far as they are useful, really measure learn- 
ing ability ("intelligence" in the sense first described), and that 
we rate individuals in intelligence through intelligence tests by 
assuming that they have been exposed to the same environment, 
in home, school and work, and that accordingly those who have 
learned the most, have the greatest learning capacity. For the 
present, however, it is safest to define "intelligence," as it is 
related to intelligence tests, as whatever intelligence tests measure. 

Instinctive reactions sometimes have been assumed to be uncom 
scious : that is, to be reflexes : and an opposition between conscious 
reaction and instinctive reaction is thus set up. Another opposi- 
tion sometimes assumed is between instinctive and volitional 
reactions. Both of these are false, and any remnant of them 
obscures our understanding of the real nature of instinct. 

There is no reason for assuming that the reactions of the duck- 
ling, when it first plunges into the water and swims, are uncon- 
scious, or even non- volitional; or that the nest-building of the 



INSTINCT AND HABIT 221 

bird or the wasp is non-volitional, or unconscious. There might 
be reason for such assumption if we knew that these animals 
were altogether incapable of volition, or of consciousness; or if 
we found in the human being, instinctive reactions which were 
unconscious. On the contrary, we find that in man, /instinctive 
reactions are characteristically conscious, and many are volitional ; 
and we are therefore forced to admit the possibility that in the 
lower animals, $f they have consciousness, instinctive reactions are 
conscious, and if they have volition, some of their instinctive 
reactions are volitional. 

As we have just said, all the instinctive reactions which can 
be studied are found to be conscious, and most of them volitional. 
The fighting reaction, whatever form it takes, and by whatever 
stimulus it is aroused, is highly conscious. The fighter is aware 
of his antagonist, and is aware of the activities he directs against 
that antagonist. He is aware of the anger, or fear, which is 
aroused by the antagonist, and if there is confusion in the fighter's 
consciousness, it is due to the vivid awareness of these emotional 
factors. Furthermore, the fighter's reactions are in most cases 
strongly volitional. He has the desire to injure his antagonist, or 
to prevent his antagonist from injuring him; this involves the 
anticipatory idea of the possible outcome, and full consent to the 
anticipated outcome in the one case, and to the escape from the 
anticipated outcome in the other. The strong rejection of an 
anticipated event is as volitional as is its acceptance. 

In -flight with fear, another instinctive reaction, there is always 
a high degree of consciousness, and a keen desire to escape antici- 
pated harm. In a somewhat different reaction, frequently com- 
bined with the fear reaction, namely, startle (being startled), 
there is perceptual consciousness of high vividness, but no voli- 
tion. Let some one fire a pistol behind your back unexpectedly. 
You " start" violently; it is by no means an unconscious reaction; 
you are keenly conscious of the sound, and your " start" is the 
reaction by which you become conscious of it. But there is no 
desire involved, and no anticipatory idea. 

If we need to consider an extreme case, the sexual reactions 
offer illustration of instinctive reactions which are not only vividly 
conscious, but strongly volitional. These reactions are very 
/ 



222 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

quickly overlaid by habit formation, but the instinctive basis may 
nevertheless be distinguished. The adolescent boy, when he 
begins to be " interested " in girls, is acting under the influence 
of fundamental instinctive tendencies. Whether he seeks their 
society and goes through the usual courting behavior, or whether 
he avoids them because of his interest," his reactions are percep- 
tually and ideationally conscious of girls, or a girl, and of a com- 
posite mass of data — visual, auditory, olfactory, tactual, — con- 
nected with girls in a direct or remote way. 

These reactions, moreover, are volitional, and it is doubtful 
if any other reactions throughout his whole life will be as strongly 
volitional as these thoroughly instinctive sexual responses. 

If there is any essential relation between consciousness and 
instinct, and between volition and instinct, it is certainly not one 
of antithesis or exclusion. The most important instinctive reac- 
tions are volitional (and, of course, conscious). We might rea- 
sonably adopt the proposal which has been made by several 
authors, that the term ' ' instinctive ' ' should be restricted to con- 1 ^ 
scions unlearned reactions, thus distinguishing them from reflexes. 
At any rate, we must distinguish these two classes from each other, 
whether both are included under the term "instinctive" or not. 

It is possible that only the conscious instinctive reactions are 
modifiable, and that the unmodinable "instinctive" reactions, 
such as those of the wasps, are unconscious. If this should be true, 
we would have a basis for classifying the wasps' complicated 
behavior as reflex, instead of instinctive. But after all, the dis- 
tinction between modifiable and unmodinable reactions is prob- 
ably one of degree. And the distinction may not hold. While it 
is undoubtedly true that only conscious reactions are relatively 
modifiable, it does not necessarily follow that all conscious reac- 
tions are modifiable, or that the degree of modifiability varies 
with the degree of consciousness. It may be that the bird, in 
building its first nest, is not only conscious, both of the materials 
it uses, and the results of its activities, but of its activities in 



soThe phrase "avoids them because of interest 7 ' is a cryptic one. The avoidance in 
this case is as specifically sex behavior towards the girls as is the frank seeking on 
the part of the other boy. The shy boy's reactions are perceptual and thought re- 
actions of girls, or of sex, and the violence of his desires and other emotions is 
responsible for the incoordination of these perceptual and thought reactions. 



INSTINCT AND HABIT 223 

building. The bird may even have an idea of a nest, 100 although 
it may have been hatched in an incubator, and never have seen a 
nest : and it may have a desire to build a nest. For there is no 
known reason why complex ideational reactions cannot be 
inherited, as well as the perceptual reactions which we know to 
be inherited. 

§5. General principle of habit formation. 

Certain general principles of habit formation have long been 
known, and were formulated before the reaction basis for per- 
ception and thought was discovered. These principles apply to 
all reactions which can be modified: to the reactions involved in 
playing tennis and billiards, swimming, and operating complicated 
machinery, as well as to those involved in studying geography 
and higher mathematics. We shall give here merely a brief sum- 
mary of these principles, or laws, of learning, leaving the more 
extended development for later chapters. 

/^ First Law. Recency 

/ The tendency for a given stimulus pattern to arouse a reaction 
which it has aroused in the past is greater, the more recent the 
arousal of the reaction by the stimulus pattern has beem> This 
tendency may be counteracted by other forces, and is most clearly 
exhibited when the reaction tendency depends solely upon the pre- 
ceding repetition. An illustration is the solving of a puzzle, which 
may easily be repeated immediately after the trick has been suc- 
cessfully done, but may be more difficult, or have to be relearned 
at a later time. Tn learning to dive, when a successful dive has 
been made, there is more chance of repeating it successfully a 
short time afterwards than a few days later. However, this result 
may be somewhat complicated by the effects of preceding unsuc- 
cessful dives, as these also tend to be repeated, and in some cases, 
where a number of unsuccessful dives have been made, the effect 
of these may disappear with increasing time-interval more com- 
pletely than the effects of the successful dive. In the " aSSOCia- 



iooOf course, the bird may be incapable of ideas of any sort. We are not claiming 
here that the bird has ideational, or even perceptual, consciousness. But there is no 
ground for denying that it has both: and if it has ideas, it very probably has innate 
ones, that is, ideas not derived from previous perceptions. 



224 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

tion test," where tlie reactor is required to respond to a spoken 
word by speaking the word first thought of, repetition of the 
stimulus word a few minutes later tends to evoke the same 
response word. This tendency is markedly lessened in the course 
of a few hours, and still more in the course of a few days, as 
demonstrated by the decreasing number of repetitions of the orig- 
inal response words to a list of stimulus words, as the time elaps- 
ing between the first and second stimulation is increased. This 
result again is not absolutely pure, since the other conditions 
which determined the response word on the first application of 
the stimulus, may remain efficacious for a certain time. 

In terms of the nervous system,( the neural pattern of a reac- 
tion tends to persist after the reaction, ready to become a path- 
way for discharge for the same stimulus pattern, but disintegrat- 
ing as time goes by, unless re-excited.) This may be figured as 
a continuity of the condition of the synapses acting in a given 
neural pattern, so that the discharge will be shunted over the same 
arcs in the same ways, when the stimulus pattern is presented 
again. With the passing of time, other reactions, using the same 
arcs, tend to modify the synaptic conditions. 

Second Law. Frequency 

The oftener a given reaction occurs as a response to a given 
stimulus, the stronger the tendency for the reaction to rexmr when 
the stimulus recurs, and the less effect the passage of time will 
have on weakening the tendency. In other words, repeating a 
reaction tends to fix it. Perfection in diving is obtained by repeti- 
tion of satisfactory dives. The repetition of a list of simulus 
words several times within the hour, if the response word for 
each stimulus word is repeated each time, increases the chance that 
the stimulus words will evoke these same response words at a 
later time. 

Third Law. Vividness 

The higher the degree of attention given to the stimulating 
object, the stronger the tendency for the same stimulus to evoke 
the same reaction at a later time. In learning the response words 
for a set of stimulus words, "inattention" is a seriously disturb- 



INSTINCT AND HABIT 



225 



ing factor; the maximal tendency to repeat the reaction is secured 
by maximal attention. This law of attention is so well known 
that little explanation should be necessary at this point. 

Expressed in neural terms, the " fixing " of a reaction pattern 
depends in an important way upon the integration of the nervous 
system in the reaction. The more completely the nervous system 
is integrated by the main arc involved, the more lasting the fixa- 
tion. 

Where several stimulus patterns are present, producing a total 
reaction, the tendency for the most vivid pattern to reproduce the 
reaction later is stronger than the tendency for the less vivid to 
reproduce it. If, for example, one is learning response words, as 
in the illustration above given, while persons are moving about 
in his field of vision, the best conditions for learning are where 
the stimulus words are most vivid. If at any moment, the visual 
paths become vivid, the fixation of the reaction to the auditory 
stimulus is decidedly interfered with. Moreover, the less vivid 
the minor stimulus pattern, the better. If, as may occur in some 
cases, a double reacion pattern occurs, so that there are in effect 
two minor systems of integration, more or less interconnected, the 
persistence tendency for each is less than that for either when 
occurring alone, and integrating the whole system in a more uni- 
tary way. One can learn spoken response words to auditory 
stimuli, while learning written responses to visual stimuli. But 
the process is seriously inefficient. Fully integrated reaction to 
the data which is to be "retained" is the optimal condition for 
fixing the reactions to those data. And this condition is the con- 
dition of focal attention to the data. 

Fourth Law. Emotional Tone 

Moderately strong emotional tone facilitates, in general, the 
formation of habits, either by increasing the retention, or fixation, 
of the reactions with which the emotion is directly connected, or 
by preventing the fixation of conflicting reactions. The discus- 
sion of the mechanism of emotion must be deferred to a later 
chapter, and hence the bare facts alone may be noted here. Not 
only pleasurable emotion, but all types of emotion have this gen- 
eral effect. And both pleasurable and painful emotions have been 



226 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

widely employed in furtherance of the learning process. Eeward 
and punishment are two practical ways of obtaining emotional 
response. 

It might be supposed that certain types of emotion favor learn- 
ing, and certain types are unfavorable. The respective merits of 
reward and punishment, for example, have been seriously argued; 
but the experimental facts bear out our supposition in this par- 
ticular case : both reward and punishment are efficacious in some 
circumstances; and there can be no reasonable doubt that all emo- 
tions are positive in their effects, provided (and this is the criti- 
cal point), they are directly connected ivitli the reactions it is 
desired to fix or to eliminate. 

In many cases, emotion is a disturbing factor, because it 
becomes connected with reactions other than the one which is to 
be learned. The boy, threatened with punishment in case he does 
not get his lesson, may be conning it over in a state of fear, or 
unpleasant anticipation, or anger, or excitement, with attention 
less on the lesson than on the future punishment, of schemes for 
evading it, or ideas of injustice, or some other ideational content. 
Obviously, if the fourth law holds, such a condition is unfavor- 
able for the learning of the lesson, however favorable for the 
learning of habits of distracted study, of sullenness, or of revenge- 
ful plotting. Pleasurable emotion may operate in a similar way, 
being connected less with the reactions with which the teacher 
wishes it to be connected than with other, in general ideational, 
reactions. 

The emotional tone, in short, is not only a positive aid to learn- 
ing: it is, because of that very fact, one of the greatest detriments 
to learning; the difference depending on its being connected with 
the reactions to be learned, or with other reactions conflicting with 
them, or which occur at such times as to interfere with them, and 
to prevent their integration in proper form. 

Fifth Law. The Limits of the Mechanism 

Since learning depends upon the integrative function of the 
nervous system, the limits of learning and the basal capacity are 
set by the inherent characteristics of that mechanism. Regard- 



INSTINCT AND HABIT 



227 



less of the principles above explained, some individuals have a 
greater retentive capacity than others, just as some are muscu- 
larly stronger than others, or have stronger hones. Within the 
retentive limit, an individual's actual retention for any reaction 
will be largely dependent upon the recency, frequency, vividness 
and emotional accompaniments of that reaction: but better results 
will be obtained by some individuals than by others. 

The limits, and general basal capacity, are dependent not only 
upon heredity, which determines the general character of the 
neuro-muscular system, but also upon the metabolic condition of 
the total organism at the time at which learning is in progress. 
The nervous system is apparently sensitive, not only to nutri- 
tional changes, and to fatigue conditions, but also to various chemi- 
cal factors, due to functions of ductless glands, and failure 
in function of duct glands, and conditions in the digestive 
tract. Just what the range of variations in the integrative 
mechanism due to chemical factors of these sorts, and just what 
the range of chemical processes capable of producing these varia- 
tions is, we cannot say. But that there are such variations is 
apparent; fatigue, sickness, indigestion, hypo-thyroidism, are dis- 
tinctly unfavorable to learning, as compared with their opposite, 
" normal" condition. 

It may well be that the organic conditions are effective through 
the modification of the conditions covered by the third and fourth 
laws. It may be that the man who never can learn as efficiently 
as another, does not succeed in integrating as thoroughly as the 
other man, or his emotions are less adequately enlisted. It may 
be that fatigue interferes with learning by inhibiting integration. 
This does not materially change the situation. It still remains 
that heredity and acquired organic conditions affect the formation 
of habits in an important way. 

Sixth Laav. Implicit Habits 

It might be assumed that the proof of a habit is the occurrence 
of the reaction. Perhaps this has been assumed by some theorists, 
but it has never been assumed by the unsophisticated man or by 
the experimental psychologist. It is true that the occurrence of 
the reaction may prove the existence of the habit (this is not 



228 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

always the case), but the non-occurrence of the reaction is no 
proof of the non-existence of the habit. One, for example, who 
has learned to dive as a child, and who has not indulged in that 
pastime for many years, may, upon "trying" again — that is, 
when stimulated by the old pattern of the water, the spring-board, 
etc., — make a perfect dive. The habit persists, and since it is 
demonstrable by the reaction, we call it an explicit habit. Another 
who learned to dive later in life, and who also has not attempted 
it for years, may, in the familiar situation, make as ignominious 
a splash as was his primitive attempt. But that does not prove 
the loss of the painfully acquired habit. It may be latent, or 
implicit. He may, on another occasion, make a perfect dive, which 
is the unquestionable result of his "practice" of years before. 
The implicit habit has become explicit. 

The existence of implicit habits is most strikingly illustrated 
in the realm of perceptual and ideational reactions. One will fail 
to recognize a person, a plant, a situation, with which one has 
earlier been entirly familiar. The formerly-established perceptual 
reaction to the stimulus pattern seems to have been lost entirely. 
Yet, on a subsequent presentation of the same stimulus pattern, 
the habit may reassert itself, and the formerly-learned perception 
may occur. The object, perhaps, is recognized; or the perception 
of it as such-and-such may take place, in accordance with the 
formerly explicit habit, without actual recognition in the true 
sense. 

In the case of "ideas," apparent "loss of memory" for cer- 
tain occurrences does not prove that "memory" is really lost. At 
a later time, the "memory" may come back. The habit upon 
which the "memory" is based was implicit: it now becomes 
explicit. The dependence of "memory" upon habit will be dis- 
cussed more fully in the succeeding chapters. 

The basis for the explanation of implicit habit, including 
implicit memory, is in part supplied by the principle of integra- 
tion: but we cannot claim that the explanation is as yet com- 
plete. Implicit habit is a fact, and must be accepted as such. The 
occurrence of implicit habit in the realm of thought has caused 
some speculators unacquainted with the mechanism of thought to 
assume a mystical! "unconscious mind," in which "ideas," con- 



INSTINCT AND HABIT 



229 



ceived as literal things, repose when not "in consciousness." One 
can see the stupidity of such an assumption by considering the 
exactly parallel case of the diving reaction. The ' ' dive ' ' you make 
today, and which is the result of your earlier learning, is not a 
"thing" which has existed all these years in some "unconscious" 
realm. It is a new act, produced today because of the habit 
formed in your nervous system years ago, and retained. So the 
"idea" which you think of today — perhaps remember where you 
put the letter you have long been seeking — is not a "thing" like 
the letter, which has been filed in the ' ' unconscious : ' ' the ' i think- 
ing" is an act, like diving, which you "learned" before, and can 
now perform adequately, even if you could not perform it yester- 
day or the day before. Whatever there may be yet to be dis- 
covered in the nervous system in final explanation of implicit 
habits, 101 there is no more mystery about them in the thought- 
reactions than in the reactions of the diving type. 

Implicit habits are perhaps based upon neural conditions 
similar to those underlying partly-formed habits. Very often, the 
continued repetition of a reaction seems for a long time to pro- 
duce no results in the way of retention, yet often the results are 
there, and the habit may be almost formed, requiring but a little 
further ' ' practice ' ' to bring it to a point where it is explicit. Many 
of us have experienced the keen satisfaction of succeeding in learn- 
ing some act, such as a stroke in a game, which has seemed hope- 
lessly beyond us until just before we "came through" with it. 
Sometimes one becomes discouraged, and gives up after long prac- 
tice, at a point where a little more trying would have caused suc- 
cess. 

Habits which have been acquired, and then have been "lost," 
or have at least sunk to such a level of implicitness that they 
will not become explicit again by mere presentation of the stim- 

101 A habit, even as it affects a single neuron involving its discharge to a certain 
neuron, or a certain group, out of all the neurons with which its axon is in synaptic 
contact, cannot be considered as resident in that neuron alone. For each neuron must 
function in a vast number of reactions, and hence in a large group of habits. Hence, 
the particular action of a given neuron at a particular time depends on the action of 
a large number of other neurons. Many conditions must be right before a habit can 
operate in a specific way and since habit is overlaid on habit upon the neuron, it 
is not surprising that habits should at times be "implicit," i. e., not quite able to 
function. 



230 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

ulus, may be relearned much more easily than they were learned 
originally. One can reacquire facility not only in games, but also 
in "intellectual" pursuits, such as mathematics, with comparative 
ease, if one has really had facility in the past. The less the reten- 
tion for what has been apparently forgotten, the greater the work 
required in relearning, and hence the relearning method may be 
used as a means of measuring retention, in cases where the habit 
has become inoperative without relearning. For example, you may 
not be able to recall or reproduce stanzas of verse which have been 
"memorized" some months ago. Apparently they have been for- 
gotten. But when you relearn them, the lessened studying now 
required, as compared with the studying required when you first 
learned the stanzas, is evidence that they were actually retained 
in part. And the difference between the former work in memo- 
rizing, and the work in re-learning, represents, or measures, the 
retention for the stanzas. 

§6. Specific problems of learning. 

When we approach the detailed problems of learning experi- 
mentally, we find that there are three distinct types of these prob- 
lems, applying to the three types of learning, viz: I. Perfecting 
a response, i. e., forming a new response or modifying an old one. 
II. Associating responses, or connecting them serially, and III. 
Simplifying a series of responses by eliminating "useless" details 
or "errors." 

I. The first type is the primary one. Connecting responses 
serially necessitates responses to be connected, although the proc- 
ess of forming and connecting may go on concurrently. Learn- 
ing the names of objects, and learning the vocabulary of a for- 
eign language, are clear types of response formation, as is also 
the child's learning to grasp objects. In some cases, the action 
involved in the new response is not new, and the learning con- 
sists in attaching it to a new stimulus. In learning a German- 
English vocabulary, for example, the saying, writing, or thinking 
of the English words is usually a familiar action; but in the learn- 
ing the action is made part of a new response for which the visible 
or audible German word is the stimulus. In such cases, there 
is usually a double response ultimately formed, namely, the say- 



INSTINCT AND HABIT 



231 



ing (writing or thinking) of the English word as a result of the 
German stimulus, and the German word-action as a result of the 
English stimulus. 

A characteristic form of response formation of the general 
type in which an "old" action is attached to a "new" stimulus 
(i. e., a stimulus which originally had not initiated the reaction) 
occurs in the substitution test. In one form of this test, a page 
is presented, on which are printed six geometrical designs (cir- 
cle, square, cross, etc.), each design occurring several times on 
the page, in irregular order. At the top of the page is a "key," 
in which the six designs are presented in a row, with a different 
letter or digit under each. The reactor is required to write under 
each design, wherever it occurs on the page, the same letter or 
digit which is under it in the key. The speed and accuracy with 
which this is done indicates the reactor's capacity for this type 
of learning. Various types of material — pictures, colors, etc., — 
may be used in this same way. In a simpler form of the test, a 
page of letters, consisting of several alphabets pied ; or a page of 
ordinary text; is presented, and the reactor is required to cancel 
certain ones by "crossing them out," with a pencil stroke. For 
example, the reactor may be instructed to cross out a and %v, 
wherever they occur. This is called the cancellation test. 

The process of building up a response is frequently studied 
in laboratories by using such a response as throwing darts at a 
target, or making a billiard shot. The imperfect response, that 
is, the response imperfectly adapted to the purpose prescribed to 
the reaction, is gradually improved by repetition. 

The range of response whose formation or modification, or 
both, is employed in the laboratory for experimental purposes, is 
extensive. The process of formation or of progressive modifica- 
tion of a response is usually described by the term practice, and 
through such practice experiments, various problems of practical 
importance are attacked. Such problems are : the determination 
of the length of time which should be devoted to practice at any 
one time; the interval which should elapse between practice pe- 
riods; the effect of learning two or several reactions concurrently; 
and so on. The results of such practice work are commonly repre- 
sented graphically by a "practice graph" (sometimes called a 



232 



ELEMENTS OF SCIENTIFIC PSYCHOLOGY 



"practice curve"), which represents the progressive changes in 
efficiency during the course of the total series of practice periods. 
Such progress may be shown in terms of the time required to per- 
form the response, or of the accuracy of the response, according 
to conditions. A graph showing the progress in accuracy in oper- 
ating an adding machine is shown in Fig. 15. 



°in\N 



8MiN 



in\u 



kniN 



5ttiN 



<vniN 



im 



aniN 



IMiN 




v^ |\^|\V^ |is^ \\^\\^ \\% xv |^ ^faA^BAVS 



Fig. 15. — Practice curve for adding machine. By permission, from W. H. Norcross. The 
abscissae represent successive practice sheets, the ordinates the times required to list and add 
on the machine each sheet. The sheets were of equal difficulty, and each contained 90 four- 
place numbers. On the first day, two sheets were worked with the left 1 hand, then two with the 
right. On the following ten days, four sheets were worked each day with the right hand. On 
the eleventh day two sheets were worked with the right hand, and then two with the left, and 
on the following ten days four sheets were worked each day with the left hand. The curve 
shows the increasing efficiency from day to day, approaching a level of maximal practice effect ; 
and also the "transfer of training" from the one hand to the other. The irregular curve at the 
bottom represents the errors. 

In experimental work, the response is always prescribed by 
the experimentor, but it is prescribed in different ways. The 



INSTINCT AND HABIT 233 

response may be described to the reactor. He is told that he is 
to hit the center of the target, or that he is to cancel each iv which 
occurs in the text. In this case, previously formed habits are 
brought immediately into play; it is assumed that the reaction of 
"trying to hit" or "marking" has been, to a certain extent, 
learned previously. The instructions then have the effect immedi- 
ately of assisting in the integration of the reactor's nervous sys- 
tem in such a way that the stimulation (target or letter) will set 
off a reaction which will attain the required set in a certain meas- 
ure (hit somewhere near the target, or mark w's with a certain 
speed). 

In other cases, the reactor is given less specific instruction, or 
none at all. This method, called the "method of trial and error," 
is necessarily applied when experimenting on the lower animals 
and on children but is also used on human adults. In the case 
of the human reactor, he is given only the general instructions of 
the end to be attained, but nothing as to how to go about it. A 
puzzle is given him to solve; or he must find his way out of or 
into a maze ; or he must find what key to press, from a large num- 
ber, in order to turn a light on. The animal, in learning to open 
a food box, is "instructed" only by his hunger and the odor or 
sight of food. After many "errors" he will make the right 
response, and obtain food. On repeated "trials," the error 
becomes less, and eventually the "right" response will be made 
immediately. 

In one form of the trial and error method, the animal is not 
required to learn any new reaction, or to modify any single 
response in an essential way, but merely to select the right 
response to make at the right point. The rat in the maze does 
not improve in ability to walk, to turn to right or left, or to per- 
form any other action, but he learns to make the correct turn at 
each point, and to walk the correct distance in a given direction. 
Learning to run a maze is comparable to the stringing of beads, 
of various colors, in a certain order. The animal is capable of 
the individual reactions : learning is a matter of ' ' stringing ' ' them 
in the proper order. According to the most recent theory of 
animal learning, this is the only form of learning of which the 
lower animals are capable. Such learning is accordingly strictly 



234 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

serial, and similar to that described under II. below. Human reac- 
tors not only learn to perform essential acts in the proper order, 
but also learn, by practice, to perfect the individual acts, and form 
new ones. 

By any method, the improvement due to practice comes down 
to three points: (1) elimination of errors, (2) increasing accuracy 
of the "right" response, and (3) increasing speed of reaction. 
The sources of the first two of these forms of improvement are 
obscure, but are apparently due in large part to the emotional 
effects of success and failure, which in some way "fix" the suc- 
cessful response, and prevent "fixing" of the unsuccessful. If 
the reactor does not know the results of his reaction, he will make 
little progress on the first two points. 

As regards the general condition of practice, the following 
points have been determined experimentally. (1) Short practice 
periods, with long intervening times, result in a saving of work 
(total practice) as compared with longer practice periods and 
shorter intervals. That is : to attain a certain level of effi- 
ciency, less work will be required, if it is done in short 
periods, separated by long intervals. Half an hour a day 
for three days gives better results than an hour and a half 
in one day. An hour every other day is better than an 
hour every day. But the limits of this advantage have not 
been determined. Doubtless there may be a practice period 
too short, and an interval too long; and the maximally effi- 
cient periods and intervals doubtless differ for different responses 
to be learned. (2) Learning of two somewhat similar responses 
concurrently sometimes decreases the efficiency in learning each. 
There seems to be "interference" in such cases. Rats work less 
efficiently on two types of problems when practicing both each 
day, than when working on either alone. In learning an English- 
Spanish vocabulary and an English-German vocabulary on alter- 
nate days, not as great progress would be made in each as when 
learned alone. But in many cases, there is no interference 
between two practice series, provided the general organic energy 
is not exhausted. Learning to swim does not interfere with learn- 
ing mathematics, if time is properly apportioned to each. No very 



INSTINCT AND HABIT ZrfO 

general conclusion can be drawn at present, as to the degree of 
unlikeness required to prevent tivo responses from interfering. 

II. The problem of serial learning lias been attacked on 
human reactors through the so-called "serial memory" procedure, 
although many other methods of attack are theoretically possible. 
In the case of animals, threading a maze is the procedure most 
employed. 

In experiments in serial memory, series of words, numbers, 
pictures, or groups of letters not making words, are presented 
visually or auditorily, and the reactor is required to "learn" the 
series, i. e., to associate them together so that they can be serially 
recalled. In the case of familiar words and numbers, the prob- 
lem is one of serial association simply, since the responses them- 
selves are already "learned." In the case of nonsense syllables, 
usually formed like TOV and NUF, by inserting a vowel between 
two consonants, the individual responses have to be learned, and 
also associated, which makes the process somewhat slower. 

Experimental results on serial associations so far bear on the 
effect of the kind of material (numbers, words, syllables, etc.) on 
the learning; and on the effect of the length of the series i. e., 
amount to be learned at one time. As might be predicted, the more 
familiar the material, the more quickly it is associated. In in- 
creasing the amount of material (length of series) to be asso- 
ciated, the work required increases much faster. Inferences from 
the results of these experiments cannot be applied directly to 
other types of learning, although unfortunately such applications 
have been attempted. The fact that doubling the length of a 
series more than doubles the amount of work required for the 
learning of the series, does not imply that doubling the amount 
to be learned in paired associations would have the same effect. 
In learning a series, each term is associated with all the others: 
and hence the number of associative connections to be formed is 
very much more than doubled by doubling the length of the series. 
In a succession of paired associates, as in learning an English- 
German vocabulary, each member of a pair is to be associated 
with the other member only. The effect of increasing the amount 
to be learned depends therefore on the conditions described under 
the concurrent learning of different things (which do not apply 



236 



ELEMENTS OF SCIENTIFIC PSYCHOLOGY 



to serial learning) and especially npon fatigue and exhaustion 
produced by the previous learning; but not upon the specific factor 
just described in serial learning. School work in history, geog- 
raphy and similar subjects is much more closely allied to the 
paired association type than to the serial type. 



__^ 



' ,' 



B 



\ 

■\- 

\ 

\ 
\ 

\ 



n 












i s 



x® 



\ 



\ .— 



\ \y d 



-*KC^CJ^21— — - - "' 






Fig. 16. — Typical pathways covered by a rat in a maze on successive trials in learning to 
reach food in the center. The rat put in the starting box, enters the maze at A and wanders 
about until he finds food at H. 



The measure in serial learning is usually in terms of the num- 
ber of repetitions, with form: and duration standardized, re- 
quired to learn perfectly a series, i. e., to make it recallable with- 
out error. By measuring the repetition required to relearn a 
series after various periods of time, the curve of forgetting for 



INSTINCT AND HABIT Z6i 

this form of learning has been determined. By learning a series 
made np of terms previously learned in a different order, it has 
been shown that there is association not only between adjacent 
terms, but also between those several places separated in the 
series. 

The influence of length of practice period, and length of in- 
terim, have not been worked out for this type of learning. 

III. The elimination of "errors" or wrong movements in a 
series may be illustrated from the case of a rat learning to "run" 
a maze (Fig. 16). The rat, entering the maze at A, wanders about, 
under the influence of hunger, and eventually finds food at H. 
Suppose that trials are made daily, each trial lasting until H is 
reached. After a few days, the rat makes the trip in shorter time, 
and begins to eliminate errors, until eventually, when introduced 
at A, he will run quickly by a definite route to H. In the figure, 
the routes of the first two trials in an illustrative case are repre- 
sented. Suppose that, on the first trial, the rat turns to the right 
at A, and on the second trial, turns to the left, but returns by a 
loop to A again. No habit is as yet fixed: the rat may, on third 
trial, turn to the right at A, then to the left at the next opening, 
and go directly to E by a route shorter than either the first or 
second. But on the first two trials, the rat has twice gone down 
the alley to the left from A ; only once down the alley to the right. 
If he repeats these two routes several more times, the effect of 
frequency alone will cause the tendency to turn to the left to pre- 
dominate, and the loop to the right will be eliminated. The same 
process will cause elimination of the loops at B, D and F. If the 
rat does not, on the first few trials, find the shortest route from A 
to E, the route A-B-C-D-E-F-G-H will inevitably be established. 

In human subjects, the elimination of error may proceed faster 
than in the rat, because of recognition. After once making the 
loop at the right of A, for example, the reactor would recognize 
the point to which he is forced to return, and the ideational proc- 
esses involved in this recognition tend to inhibit the tendency to 
repeat the loop excursion on future trials. Although the precise 
nature of the recognition reaction is at present unknown, it is an 
important factor in human learning, and apparently entirely ab- 
sent from the reaction of the rat and other infra-human animals. 



CHAPTER XII 

THE DEVELOPMENT OF PERCEPTION 

§1. Direct and indirect perception. 

Perception has been described in the loose terminology of the 
Anglo-German psychology, as " sensation plus imagination," with 
the further qualification that the pure sensation never (or seldom) 
occurs. In this formula, "sensation" means not the sentiendum, 
but the awareness of the sentiendum: which we have called, so far, 
sense perception: and perception means the being aware of com- 
plex objects, as including more than the sentienda which can 
actually be "sensed" at the moment of perception. Interpreted 
in such a way as to give the greatest intelligibility, the formula 
means that (1) perception, as it normally occurs, is more than 
sensation: and, (2) that the additional factor is imagination, or 
imagining. The first proposition is true; the second is false; and 
the best way to avoid confusion is to ignore the formula and con- 
sider the process of perception, as we have so far, as a reaction 
process. 

We have been considering perception, up to this point, in its 
analytically simplest form, as the awareness of sentienda actually 
"presented" to the senses, ignoring the fact that we are usually 
aware, in such cases, of more than these immediately presented 
sentienda. We perceive color, for example, when certain visual 
stimuli act upon the retinal receptors ; but in such cases we rarely 
perceive color alone: we perceive a colored object, and the object 
includes factors other than color, although these factors, in such 
a process of perception, are not presented to sense; that is, they 
correspond to no stimuli actually affecting receptors. It is now 
necessary to examine into the way in which such perceptual proc- 
esses may arise. In this examination we must keep empirical facts 
constantly in view, and refer all our formulations to these facts. 
It is an easy matter in psychology, perhaps easier than in other 
sciences, to devise a set of terms, and then proceed to shuffle 

238 



THE DEVELOPMENT OE PERCEPTION 239 

these terms, using them in a Logical game much as the pieces are 
used in the game of chess, losing sight of the realities these terms 
are supposed to represent, and arriving finally at formulations 
which very much misrepresent the facts. This unfortunate result 
can be avoided only by a strict adherence to empiricism. 

Let us consider a simple case. Suppose that an orange of a 
ripe color is placed before your eyes. That which you see, strictly 
speaking, is just the color and the spatial form. But you perceive 
more than that: you perceive an orange: and an orange is much 
more than a spot of color. In order to be an orange, the object 
must have odor, taste, weight and certain tactual characteristics; 
and if your previous experience with oranges has been extensive, 
you perceive these characteristics with some degree of vividness, 
when you perceive an orange, although the only details sensed 
may be the color and space-form. 

Suppose, for another illustration, that you hear the voice o\' 
some one in the next room. The sensed, or directly perceived, 
content is composed of sounds of certain pitches and timbers ; but 
the total content actually perceived includes other (indirect) ele- 
ments, perhaps visual, which make the sound the roiee of a eer- 
tain person, or at least the voice of a certain kind of person. 

In the case of most sounds, it is easier to identify the total 
percept (the total content perceived) than it is to identify the 
directly sensed sound alone. If several plates are dropped in the 
kitchen, that which you, in the dining room, recognize first, is that 
chinaware has been smashed. A certain eerie note from next door, 
you recognize as the wail of a violin, as soon as it "enters" your 
consciousness. In neither case do yon recognize the sound as such, 
and then refer it to the proper complex object. In many such 
cases, it is impossible to identify the sound at all by its intrinsic 
characters of pitch and timber, and it is recognized only by the 
indirectly perceived factors in the content. Very often, words 
spoken hj one person are heard by another but not heard as 
words. The hearer merely grasps the meaning. This is the ex- 
planation of many cases of "mind reading," in which words 
whispered by one person, who does not know he is whispering, 
are heard by another, ayIio does not know that he hears, but catches 



240 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

the idea nevertheless, and catches it by a response to the auditory 
stimulation of the words. 102 

The process by which the content of perception initiated by 
various stimuli becomes complicated by the addition of indirectly 
perceived content to the directly perceived or sensed content, is 
to be designated as the development of perception. It would be 
simple to assume that the experience of the infant begins with 
sensing, or direct perception only; and that his perceptions are 
progressively built up from that level to the complexity of adult 
life: that all objects seen by the infant are at first, merely color 
and form, and later acquire the complexity which makes them 
really objects, through the continued experience of the various 
factors. This assumption is, however, unwarranted, since the con- 
siderations of instinct and heredity justify the contrary assump- 
tion, namely: that the infant begins his perceptual experience with 
certain perceptions which are complex from the first. It is never- 
theless a fact that the infant's perceptions are less complex than 
those of the older child, and that a process of perception build- 
ing goes on throughout childhood, extending with lessening activ- 
ity well into adult life; and we may legitimately assume that the 
further development of these perceptions proceeds in exactly the 
way in which it would if these perceptions had actually been built 
up or developed from really "simple," direct perceptions. 

The infant's visual perception of an orange perhaps from the 
very first, includes more than the mere perception of color and 
visual form: how much more it is impossible to determine, al- 
though it is probably very little. In whatever stage of the de- 
velopment the infant's perception starts, it goes on developing 
from that point exactly as if it had been built up to that point 
from the very simplest stage. We may then illustrate the general 
process of perception building by tracing the development of a 



i02ln terms of the explanatory theory given below, these facts mean that there is, 
in the cases cited, no reaction for the sound as such, but a reaction for the total 
complex of content of which the sensed sound is but a part; and that this reaction 
is initiated by the sound stimulus alone. It might also be initiated by the visual 
stimulus alone. Of course, reactions for the perception of mere sound may be built 
up; but there is little occasion for the building of such reactions in the experience 
of the ordinary man. 



THE DEVELOPMENT OF PERCEPTION 



241 



certain perception from a hypothetical starting point at which it 
includes nothing indirect, but only the directly sensed details. 

Let us suppose that an orange is presented to the infant's vi- 
sion, producing a reaction from which we may infer that the color 



Receptors 



Brain and 




Effectors 



Olive Slater 

Fig. 17. — Scheme of the pathways and interconnections involved in the development of die 
perception of an orange. The heavy lines v-V, g-G, t-T, m-M', and o-O represent the assumed 
primary reaction-arcs from the visual, gustatory, tactual, kinesthetic, and olfactory stimuli 
respectively. The lighter lines represent the cerebral interconnections formed- between these 
primary arcs. 



of the orange, at least, is perceived. The visual stimulus we will 
indicate by v, the resultant action by V. Suppose that later the 
child is allowed to touch and handle the orange, with resultant 



242 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

instinctive reactions. The tactual stimulations we will indicate 
by t, and the muscular stimulation by m: the corresponding re- 
actions by T and M. The olfactory stimulations from; the juice 
and peel, o, lead to still another reaction, 0, and the gustatory 
stimulation, if juice is taken in the mouth, to the reaction G. We 
may neglect, for purposes of simplification, the possible tempera- 
ture and visceral stimulations. 

Since some of these reactions will at times occur simultane- 
ously, as well as in immediate sequence, the neural parts of the 
reactions will tend to become interconnected, through the integra- 
tion of the central nervous system, so that eventually they become 
several phases of a total reaction, and this total reaction may be 
produced by any one of the several stimulations which were 
originally necessary to produce all the reaction details. The child 
comes thus to perceive not mere color, but orange, when the orange 
is visually presented; not mere odor, but orange, when it is pre- 
sented to the olfactory receptors alone. He may even perceive 
it as an orange when he feels it with his hands, without visual 
or olfactory stimulation; and he will therefore mistake other 
round, heavy objects for oranges until he learns to make the 
orange-reaction only when factors in addition to the shape are 
experienced. 

Although we may call the perception of the orange, which is 
initiated now by visual stimulation, now by olfactory stimulation, 
and now by tactual stimulation, the same in each case, because 
in each .case it is the perception of an orange ; yet the three cases 
may present important differences, in that in one case the visual 
qualities, in another the olfactory, and in the third the tactual, 
are most vivid. The orange-reaction, therefore, is not assumed 
to be precisely the same in the three cases, but may have in each 
case one of the original reactions more pronounced than the other 
two, although all three original reactions are involved in each 
case. 

There is, indeed, a wide range of variation in a single per- 
ception of this kind. In certain cases, the importance of the sev- 
eral direct and indirect factors may be significantly different, and 
the non-visual qualities may, in some cases, be more vivid than 



THE DEVELOPMENT OF PERCEPTION 



248 



the visual, although the visual content is direct, the other indirect. 
When the several direct sensory reactions have become amalga- 
mated into a single perception, the exact details of this percep- 
tion will be determined, not by the characteristic sense stimula- 
tion of the object alone, but by it in conjunction with the various 
other stimulations playing upon the receptors of other senses, and 
by the reactions (whether perceptual or ideational) which have 
preceded. The perception, even at the moment when it occurs, 
is not an isolated result of a restricted series of previous reac- 




18. — Hidden figures. (O. C. Slater, after Gudden's "Children of the Brain.") An illustration 
of the effects of previous reactions in determining' the indirect factors in perception. 



tions, but is connected with the whole complex of mind through 
the integration of the nervous system. 

Along with the integration of the original perceptual reac- 
tions, goes a simplification and transformation of the reactions. 
Originally, the various orange-reactions involve extensive move- 
ments of all the limb muscles, and most of the other muscles. 
These activities are reduced, and eventually transferred to muscles 
which, at first, have a minor share in the reaction, namely, the 
vocal muscles. The most important part of the orange-reaction 
the child acquires in the course of time is the speaking of the word 



244 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

' ' orange." In the perceptual reactions of both children and 
adults, language plays a role of very great importance. 103 

Whether in the process of development, perceptions ever reach 
a stage in which the muscular part of the reactions become elimi- 
nated entirely, we cannot now say. This is possible; and we may 
even make a guess at the mechanism by which the muscular activ- 
ity is supplanted; but the discussion should be deferred until 
thought reactions have been discussed. In the development of 
perceptions, that is, during the process of learning, the muscular 
activities are certainly necessary; and if they are eliminated in 
some cases, the perceptions become thereby fixed in form, and 
cannot be further modified, except by a reinstatement of the com- 
plete reactions, that is, by the re-entry of the muscular activities. 

In order that a perception may be as definite and vivid as pos- 
sible, the muscular part of the reaction must be decided and defi- 
nite. This principle has a wide range of practical application, 
and is nicely exemplified in the reading and transcribing of num- 
bers. If one is engaged in reading numbers of several places on 
one sheet, and writing them on another, long numbers may be car- 
ried over without error if they are read aloud, or even if read 
silently with distinct vocal movements. If read with little mus- 
cular activity, as many people normally read (perhaps, as above 
indicated, in some cases with none) mistakes are much more lia- 
ble to occur. 

§2. Discrimination. 

Discrimination is one of the most important aspects of the per- 
ceptual process. We have assumed, in the foregoing pages, the 



io3The importance of the language reaction for perception, as well as for thought, 
is indicated by the fact that in any complete language, such as English, there is a 
word, or a word combination, for practically every thing which can be perceived or 
thought about, and that progress in accuracy in perception and thought goes hand 
in hand with progress in accuracy in the use of language. How slight may be the 
significant differences in reactions is indicated by the slight, but important, differences 
in words: beat, bate, bet, bat, but, boat, bought, boot, bite, bit, differ slightly in 
sound, and the differences in the reactions which produce them are slight; yet the 
educated man seldom slips, and makes the exact reaction required — speaks the right 
word for each occasion. 

It must not be supposed that even in the case of the adult, the language reac- 
tion is the only reaction for the highly developed perception. All the striped muscles 
take part in one or another of our perceptions, although the language reactions rise 
in relative importance as perceptual discriminations we make become finer and finer. 



THE DEVELOPMENT OF PERCEPTION 245 

fact of discrimination, without attempting to explain it. Differ- 
ence thresholds of all kinds, for example, depend upon the reac- 
tor's capacity to discriminate intensities, qualities, positions and 
magnitudes: that is, to distinguish, in respect to some character, 
between two data which are very closely similar in that char- 
acter. 

The capacity to discriminate accurately where the actual dif- 
ferences are small is not the sole factor in "intelligence" or 
"mental capacity," but it is a very important one. The musician 
must be capable of fine discrimination of pitches, timbers, dura- 
tions, and intensities. The artist must have keen discrimination 
of hues, saturations, and brightness. The important discrimina- 
tions of the politician and the business man are more complex, and 
less capable of measurement, but none the less vital. 

Discrimination in any specific case is nothing more nor less 
than accurate perception : perception of something as this, and not 
that. The capacity to discriminate is therefore fundamentally 
the capacity to make, in precise fashion, one reaction to one situa- 
tion or object, and another reaction to a situation or object slightly 
different from the first. Learning to discriminate is the develop- 
ment of reactions essentially different, to definite, but only 
slightly different, stimuli. If, for example, I cannot discriminate 
between the note of 256 and the note of 259 vibrations per sec- 
ond, it is because I cannot make my reaction to the one always 
different from my reaction to the other, but am obliged to make 
the same reaction to both, or if I make two or more reactions, I 
make these reactions indifferently to either stimulus. If, by prac- 
tice, I learn to discriminate between these two notes, what I really 
learn is to make one reaction (which may be the vocal reaction 
of saying "lower") to one, and another reaction (perhaps the say- 
ing of "higher") to the other. The invariable law is: If I can 
discriminate between two things, I can make different reactions to 
them. The proof of this law is that I can apply different names 
to whatever I can discriminate; for naming is one form of re- 
acting. 

The converse law, that whenever I make different reactions 
to two objects, I am discriminating them, may not be so easily 
proven, but it is inescapable. The only point of difficulty con- 



246 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

cerns unconscious reactions, which we exclude from consideration. 
We speak of discrimination only when the reactions are conscious 
and different. The fact that our reactions to the same thing may 
show considerable variation is not a stumbling block. It is only 
where there is systematic variety, so that the reaction is differ- 
ent to the different objects, over and above the irregular varia- 
tions in both reactions, that we speak of discrimination. 

It is significant that where we find it important to discrimi- 
nate between two objects, classes, or events, which have previously 
been treated as the same, or equivalent, a difference in reaction 
to the two must be introduced at once. In some cases, as in sort- 
ing colored papers, where first it has been sufficient to put all 
green in one pile, but now becomes important to distinguish be- 
tween yellow-green, neutral-green, and blue-green, the differences 
in reactions are in part gross differences in reaction of limb or 
trunk muscles: putting them in different piles. In other cases, 
difference in word-reactions become the critical differentia. When- 
ever we decide to discriminate between two plants, animals, min- 
erals, or theories, hitherto not distinguished from each other, we 
have to apply a new name to one of them; and this involves the 
formation of a new word-reaction to one of the objects. 104 

§3. Illusion. 

From the fundamental facts concerning the development of 
perception, if no additional information were available, we would 
be compelled to infer that perception is not always true: not only 
that one may fail to perceive indirect content which properly be- 
longs with the direct or sensed content, but that one may dis- 
tinctly perceive indirect content which is not really a part of the 
object at all. 

The first form of inaccuracy; incompleteness of perception; is 



io4The formation of a discriminatory reaction may be illustrated from pictures in 
which there is a "hidden" content. Figure 18, for example, may he perceived as 
merely a picture of a "brain," in which case the reaction is practically the same as 
that to a slightly different stimulus pattern in which there are no ' ' hidden ' ; babies. 
After the different reaction of perceiving ' ' babies in the brain ' ' has been made once, 
the picture will thereafter be perceived by that reaction, and not by the one by which 
mere "picture of a brain" is perceived. The differences in the two reactions are, 
for many persons, verbal, that is, speech-action differences: but they may be differ- 
ences in the reactions of muscular systems other than the vocal. 



THE DEVELOPMENT OE PERCEPTION 247 

indeed the rule, rather than the exception. Rarely, if ever, does 
one perceive every detail in an object of consciousness. The build- 
ing up of perception does not, in general, reach such a stage of 
meticulous completeness. Nor would it be practically useful to 
do so. The optimal condition is the perception of those factors 
which are important for thought and action, and omission of the 
perception of those details, in objects and situations, which are 
relatively unimportant for further reactions. What is important 
for one person, or at one time, may not be important for another 
person, or at another time. 

The second form of inaccuracy, illusion, or the perceiving of 
what does not exist in the form in which it is perceived, is also 
common, and is in general a source of danger to practical life, 
although it may not always be a detriment. Incomplete percep- 
tion and illusions are due to several different causes, which are 
briefly described below. 

I. Imperfect development, or wrong development, of percep- 
tion. In learning to perceive, before the integration pattern is 
well established, the reaction is apt to be imperfectly discrimina- 
tive, as when the child above referred to perceives a ball as an 
apple. In other cases, the learning process may firmly establish 
a wrong perception. Such errors are wholly matters for correc- 
tion through education. 

The various objects which, for practical purposes, should evoke 
the same reaction, are not all precisely the same. They do not 
stimulate the sense organs in precisely the same way. Yet, the 
reactions, in many cases, should be the same. The large, sym- 
metrical apple, for example, and the smaller, crooked apple, 
should cause, in many circumstances, the same reaction. Both 
should be called "apple" (vocal reaction), and should be peeled 
in much the same way. Under some other circumstances, the re- 
action should be different. In selecting fruit for the table, the 
small, crooked apple should be placed in one dish; the large, sym- 
metrical one in another dish. Under these circumstances, one 
would be called "perfect apple," and the other "imperfect apple." 
The differentiation of the reactions would be brought about in 
part by accessory sensory stimuli; in part by ideational reactions 
preceding the perceptual. 



248 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

So, too, the child should make, under some circumstances, the 
same reaction to the apple and the ball. He should catch the one, 
when tossed to him, in the same way as that in which he catches 
the other. Yet he should not try to eat the ball, nor call it apple. 
Erroneous perception, in cases such as this, consists in making 
to one object, the reaction appropriate to a somewhat different 
object, in cases where it is more useful to make a different reac- 
tion. 

II. Different objects may stimulate the receptors in ways so 
nearly alike that differential reactions can never be built for them. 
That is to say: there is no possibility of discriminating them, and 
a properly developed perception is brought about by the wrong 
object. Illusions of this sort are most striking in the realm of 
space perception, although they are found in various realms of 
experience. The illusion of depth produced by the pictures in a 
stereoscope is due to the fact that the images of the two pictures 
on the two retinae are precisely such as a real scene, having depth 
instead of the flatness of the photograph, would produce. Even 
in single pictures, the artist, by making the details such that the 
stimulus to the eye is closely like that which would be produced 
by real objects and distances, is able to give an illusory percep- 
tion of depth or solidity. Other illustrations may be found in 
the realm of sound. If two persons' voices are indistinguishably 
different, either person may be perceived, upon hearing the voice 
of either. 

III. Perception of a complete object may occur, when actually 
only parts or fragments of an object are presented to the sense 
through which these fragments are perceived. A person in dark 
clothing, seated before a dark screen, from which a large part of 
the clothing is indistinguishable, even with close attention, is fre- 
quently perceived as a complete person, and no notice is taken 
of the fact that a large part of the figure is indistinguishable. 
The face, hands, perhaps the feet, and certain parts of the cloth- 
ing being perceptible, and in the natural relation to one another, 
the whole figure is perceived. This form of illusion is frequently 
employed in pictorial advertisement, where for example, a few 
details of a woman, clearly presented, cause perception of a woman, 
and not perception of detached parts of a woman. Various other 



THE DEVELOPMENT OF PERCEPTION 249 

illustrations of the completion of objects in this illusory way may 
be found if we look for them. This form of perception is differ- 
ent from the ordinary cases only in that the indirectly perceived 
content is content which, if presented, would be content for the 
same sense through which the direct content is perceived. Cer- 
tain visual details, for example, when presented, cause the per- 
ception of other, nonpresented visual details. In the case of the 
perception of the orange described in section 1, indirect details 
were assumed to be of modes other than those directly perceived: 
but the method of perception is the same in the two cases. A 
part of the total, original stimulus produces the complete reac- 
tion. 

IV. The reactions to certain objects, and hence the percep- 
tions of these objects, may be modified by stimulations due to 
other objects simultaneously present. The length of lines, or their 
directions, may be wrongly perceived because of the effect of other 
lines in the field of view, although the actual stimulations from 
the wrongly perceived lines are not modified thereby, and al- 
though these stimulations are not the same as would be produced 
by lines of the length or directions perceived. Errors of this sort 
are most conspicuous in the field of vision, although they un- 
doubtedly exist in all departments of perception. 

"Contrast" effects in magnitude of area, as when rectangles 
are compared with each other, are also found. A square of one 
inch diameter looks smaller when placed between two large 
squares than when placed between two smaller ones. Contrast in 
brightness in some cases is due to the same sort of reaction modi- 
fication; a square of gray looks darker on a white surface than 
on a black surface. In some cases, this effect is enhanced by actual 
adaptation change in the retina, but it can be obtained under cir- 
cumstances which exclude adaptation. Certain color combination 
effects also are, perhaps due to the same sort of cooperation of 
stimuli. 

Certain letters in a word may be wrongly perceived, and the 
word read as if spelled with the substituted letters, because of 
the stimuli due to other letters of the word. It is partly on this 
account that accurate proof reading is' difficult. One wrong letter 






250 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

jfi the body of a word is seen as if right, because of the stimula- 
tion of the other letters. 

This influence of simultaneous stimulation is widespread. A 
painted ball, which alone would not be perceived as an orange, 
may be "mistaken" for (wrongly perceived as) an orange, if the 
word orange is spoken as, or just before, the object is presented. 
And this occurs without any "ideas" intervening. A scarecrow's 
head, topped by a sure enough hat, and just showing above a wall, 
may he perceived as a man's head, where the hatless head would 
not he so mistaken. A polished monkey-wrench, held by sonic 
one in the position of a pistol, may he perceived as a pistol, in 
spite of the large visual difference between the two articles. 

These effects are really illustrations of the general principle 1 
of integral ion, and of the particular aspect of the principle which 
is, that undoi- normal conditions, our reactions are not to single 
stimuli, or small groups of stimuli, hut to large slimulus-patterns, 
involving all of 1 he senses. 

V. Failures to integrate the direct content are in a large and 
important range of cases responsible Cor wrong perceptions. The 
person tails to notice details which are directly presented, and 
which it noticed, would exclude the wrong perception. This is 
the grand source of errors in testimony on the witness stand, or 
off of it; and the success of the sleight of* hand performer and 
the spiritualistic "medium" is due directly to it. The causes of 
this failure of integration are numerous and variable. In many 
cases, they are thought-processes, which have their origin in 
earlier stimulations, or they are strong emotional reactions. The 
man who has been led by his desires, or by skillful suggestion, to 
expect to perceive certain things which are to he presented in 
part directly and in part indirectly, will usually perceive those 
1 hi ngs; and the direct factors which would prevent the percep- 
tion of that particular indirect content will not be perceived. 
Aside from any thought processes initiated previously, emotions 
of astonishment, fear, anger, horror, etc., so involve tin; integrat- 
ing mechanism as to prevent the complete perception of stimula- 
tory factors, and hence several witnesses of an unexpected event 
may have totally different perceptions. The Fallibility of testi- 
mony due to these causes is well known. 



THE DEVELOPMENT OE PERCEPTION 251 

The sleight of hand performer (prestidigitator or magician) de- 
pends in part upon arousing ideas which will facilitate imperfect 
perception; but in largo part he employs purely perceptual means. 
By movements of bis wand, hands, head, or body, or by the activ 
ity of his stage assistants, he " directs attention" to the details 
he wants to be seen, and away from details he does not want seen. 
This phrase "directs attention to" means nothing but the Pad 
that by definite accessory visual stimulations, lie causes certain 
parts of the total visual object to integrate the nervous systems 
of the spectators, so strongly that the transits belonging to cer- 
tain other parts are completely drained off into the dominant 
transits, and these objects reduced to the lowest limits of vivid- 
ness. In the total stimulus-pattern, only a Limited part is effica- 
cious in determining the details of the reaction. The afferent cur- 
rents from the remaining stimulations, although integrated into 
the total discharge-pattern, serve only as general increments to the 
total current How, and exercise in the total reaction none o\' the 
tendencies toward definite reactions which they would exercise if 
acting alone. 

Much the same situation arises in the case o( the sudden and 
unexpected event: the automobile accident, or the murderous at- 
tack. Here, through the suddenness or the intensity of certain 
stimulations, other stimulations are "crowded out:" their affer 
ent currents are completely assimilated in the general integration. 
In the spiritualistic seance, ideas, of an anticipatory kind, play the 
leading role. 

VI. Emotion and expectation are productive of illusion even 
when failure to perceive sensory content is not an important con- 
dition. A sound may be heard as coming from the expected direc- 
tion ov object, although nothing is offered to sense, which could 
produce a perception of any direction. Ventriloquism depends 
upon this tendency. Ghosts are also largely due to the same 
cause: certain fragmentary visual presentations being supple- 
mented with the indirect details essential to a spectre. It is, how- 
ever, true that in many cases of ventriloquistic and spectral illu- 
sions, there are stimulatory details which would destroy the illu- 
sion if \\\c] were perceived, the illusion being really of the type 
describ' d under IV above. 



252 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

§4. The conditions of accurate perception. 

The consideration of illusion outlines sharply, by a process of 
elimination, the conditions under which perception is most ac- 
curate: the conditions, therefore, most satisfactory for scientific 
observation. The maximally disturbing factors are strong emo- 
tional states, biasing ideas, unexpected stimuli, and lack of train- 
ing. These, it is obvious, must be excluded as far as possible. 

Training in the specific type of observation required may be 
obtained, and is essential. A high degree of training in one line 
of observation is not sufficient preparation for observing along 
another line. Sometimes it is a positive disadvantage. The botan- 
ist, however highly trained in the observation of plants, is not 
qualified thereby for the making of psychological observations, 
and, conversely, the training of the psychologist, however 
thorough, does not fit him for botany. Long and thorough train- 
ing in the mathematical aspects of physical science is apparently 
a positive impediment to observation in certain lines of psycho- 
logical investigation: this, at least, seems the only explanation of 
the fact that the scientists who are dupes of spiritualistic mediums 
and of the demonstration of telepathy, levitation, and kindred 
mystical forces, are almost without exception mathematicians, 
physicists and engineers. 

The avoidance of emotional disqualification is not a simple 
and easy matter. To a large extent, the emotional tendencies of 
the individual are hereditary, and not greatly modifiable. Yet 
some improvement may be made here by a technique which can 
be described here, which will be made intelligible by later con- 
sideration. First of all, one must obtain a clear idea of one 's emo- 
tional difficulties, and must then form and think attentively, from 
time to time, the idea of being free of these emotional faults. 
Really, such a process is an act of will, of the typical sort. To 
the anticipatory idea of certain emotional traits is added the de- 
sire of possessing those traits, and assent to the desire. The ef- 
fect of such volition may be large or small, but as we can see from 
the standpoint of the relation of nerve integration to action and 
consciousness, an effect certainly will be produced. The excitable, 
impulsive man can become less so by willing to be ±°ss so; and 
the depressed, apathetic man can become more sanguine if he 



THE DEVELOPMENT OF PERCEPTION 253 

wants to. Of course, the removal of the conditions, whether 
environmental or physiological, which predispose to detrimental 
emotional states, is the first consideration. The scientist, whose 
work suffers from emotional faults due to unhappy family life, 
improper food, use of alcohol, or excessive thyroid secretion should 
first remove these causes as far as possible, before attempting 
4 ' self control." One removes as many obstacles as possible from 
the road before overhauling the engine in preparation for the 
climbing of the difficult grade. 

Biasing ideas are the more common sources of defective ob- 
servation in scientific w^ork, and in less formal perception. If you 
have a theory of what should happen under certain conditions, 
you are very apt to overlook details of the real happening, and 
to supply details falsely, in so far as the real details do not fit 
your theory, and the fictitious ones do. Moreover, you are pre- 
disposed to overlook defects in the conditions of the happening, 
and assume that the actual conditions, which may produce the 
expected happenings, are the conditions which your theory as- 
sumes. Much defective scientific observation has resulted from 
such ideational error. The removal of bias is a procedure very 
similar to the improvement of emotional conditions: in fact, the 
predisposition to bias is largely an emotional matter. The ivill 
to be unbiased is the efficacious thing, and this will must be based 
on a clear understanding of the nature of scientific hypotheses. 
We need to remind ourselves frequently that hypotheses are only 
suppositions made in order to be tested, and we need to remind 
ourselves also of the importance of being as pleased at finding 
that a hypothesis does not "work," as at finding that it does 
"work," even though we have constructed the hypothesis our- 
selves. Only through the active will to be unbiased: the will to 
have no emotional attachment to hypotheses, and to expect ob- 
servations to substantiate them no more strongly than we expect 
the observations to disprove them: can the observer attain to an 
impartial attitude. 

The avoidance of unexpected stimuli is the outstanding func- 
tion of scientific method. Observation of uncontrolled events is 
useful in science, principally as a means of suggesting hypotheses 
and experiments. But experiment is the real foundation of 



254 ELEMENTS OE SCIENTIFIC PSYCHOLOGY 

scientific certainty. Having formed a hypothesis, we proceed to 
arrange the conditions so that a certain group of events will hap- 
pen: certain data will be produced. Foreseeing the event because 
we have arranged it, we are prepared to make a definite discrimi- 
nation, namely, to observe whether a certain definite event does 
or does not occur as a part of the phenomenon: whether a cer- 
tain datum does or does not appear. The integrative mechanism 
is prepared to react in one of two definite patterns, to be deter- 
mined by the presence or absence of a definite detail in the stimu- 
lation pattern. 

The difference between experimental observation and uncon- 
trolled observation may be illustrated from the murderous attack 
previously mentioned. Several witnesses of a shooting affray may 
differ in their testimony as to which of two men drew his gun 
first. The unexpectedness of the event prevented accurate obser- 
vation, and there is no necessary implication of mendacity on the 
part of the disagreeing witnesses. If, however, these witnesses 
had been posted in advance in positions favorable to observing 
the shooting; if the point, direction and moment of encounter of 
the principals were known in advance to the witnesses; and if 
they had been instructed to watch for this one specific detail, and 
to record their observations at once; they should agree in their 
reports. The unanimous testimony should be that A drew his 
gun in response to B's drawing, or commencing to draw; that B 
drew in response to A's drawing, or beginning to draw; or that 
both drew on sight, without either waiting for the action of the 
other. Discrepancy in the report would mean that one or more 
of the witnesses are gravely defective in vision or in intelligence: 
or else that one or more are lying. The degree of certainty which 
we may allow to the report of any one observer, either in every- 
day affairs or in the laboratory, depends upon the truthfulness of 
the observer, and the degree . of control actively exercised over 
the events on which the report is based. 

§5. Meaning and symbolic perception. 

It is possible" to discriminate the direct content from the in- 
direct content in perception, and in that case we call the indirect 
content the meaning of the direct content. In the case of an orange 



THE DEVELOPMENT OF PERCEPTION 255 

visually presented, for example: the disc of color, which is the 
whole of the direct content, may be discriminated from the 
solidity, weight, odor, juiciness, sweetness, and whatever other in- 
directly perceived content gives the disc the orange character- 
istics, and we then say that these are the meaning of the visual 
presentation; or, we say that the disc of color means an orange. 
Conversely, the color disc is the symbol of the orange. 

These terms are seldom applied, however, to the simple cases 
of concrete objects, that is, to objects such as the orange^which 
are composed of data localized in the same space. Eather we 
tend to restrict the usage to cases of complex objects, or contents 
which are composed of a concrete object (the symbol) together 
with other objects related to it in a variety of ways, other than 
by spatial coexistence. The name of an object, for example, is a 
symbol, and the object is its meaning. The American flag is the 
symbol of the nation, or of a certain group of national character- 
istics. In perceiving the flag, we perceive more than a striped 
piece of cloth hanging from a rope. One perceives it as the Ameri- 
can flag; and so, one perceives the name of Napoleon Bonaparte, 
not as the mere sound which it is for the auditory sense alone; 
one attends little to the sound, but perceives the name of an ad- 
mirable military commander or of a cruel monster (according to 
one's historical viewpoint). One does not discriminate between 
the symbol (the sound) and the meaning (the perceived character- 
istics) : one perceives the two as a unified content. Discrimina- 
tion is possible, however; we may by a series of thought reac- 
tions, separate the direct from the indirect content, as we are 
doing here, and set the symbol over against the meaning. 

In the use of names, we are producing perceptions which dif- 
fer very much from those to which we have hitherto confined the 
discussion. In the early perceptions of the child, and in our own 
perception of many concrete objects, the direct content is focal in 
consciousness. In the perception of objects through names, the 
name itself, if familiar, that is, if it has been reacted to frequently 
in the same way, is usually out of the focus, and the meaning is 
focal. This sort of presentation pattern is not essential to symbol- 
ism : in perceiving the flag, for example, the visual details are usu- 
ally focal; and even in perception based on names, the name may 



256 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

be focal. But the non-focal perception of a symbol is frequent, 
and in some cases the symbol cannot be made focal, although the 
perception based on it may be definite and important. In such 
cases, it is convenient to call the symbol a sign, reserving the term 
symbol for the cases in which it may be focal. 

Suppose that in the course of a conversation with some per- 
son you inadvertently make a remark which especially interests 
him, or which irritates him, or pleases him. In many such cases, 
if you are looking at his face, you perceive that he is interested, 
or irritated, or pleased, although you do not know ivhy the re- 
mark had the effect it did have. In such cases, it is frequently 
impossible to detect the sign of interest, irritation, or pleasure. 
Yet, the sign existed, as a change in his face, which stimulated 
your vision in such a definite way as to produce the perception. 

We cannot say that it is impossible that one might learn to 
perceive such signs. We should rather incline to the assumption 
that it is possible. Nevertheless, most persons have not learned 
to make the discrimination, and the attempt to do so — to catch 
the facial changes as facial changes — uniformly interferes with 
accurate perception of the meaning. 

The pseudo-science of character analysis furnishes copious il- 
lustration of the possibility of perceiving meanings without per- 
ceiving the signs thereof. Character analysis began as phrenology: 
the theory and practice of reading traits of emotional character, 
and mental capacities, from the " bumps" or superficial details 
of the skull. Although this brand of character analysis is still 
actively exploited, it has been overshadowed of late by newer sys- 
tems which read "character" in the shape and line of the face; 
the size and form of the nose, mouth, eyes, and even the color of 
the hair and eyes, and other like details. Of course, such "char- 
acter reading" is impossible: an elementary knowledge of psy- 
chology and the laws of heredity assures us of that: and the pos- 
sibility of developing any such system is too small to be seriously 
considered. Yet the systems flourish, and their apostles wax fat 
on them. 

The explanation of the financial success of the promoters of 
certain systems of "character analysis" is in part similar to that 
of the persistence of spiritualism. The dupes never really check 



THE DEVELOPMENT OF PERCEPTION 257 

up on the claims of the exploiters. Corporations pay thousands 
of dollars to clever exploiters, for the "character analyses" of 
their employees, and in many cases pigeon-hole the findings, while 
in cases where some attempt is made to use the findings, no scien- 
tific estimate of the practical outcome is made. Yet, it seems prob- 
able that some "character analysts" do make shrewd estimates, 
with a certain validity, of the characteristics of some of their 
patients, and that these cases impress persons who observe them. 
Most of us, as a matter of fact, make "character estimates" 
of our friends and acquaintances, and even of chance met indi- 
viduals, and some of us have more nearly accurate perceptions of 
this sort than do others. But we make these estimates, just as 
we observe the emotional changes in others, without discriminat- 
ing or identifying the signs at the bases of our perceptions. Any 
serious attempt to discriminate signs, in the present state of scien- 
tific knowledge of the subject, interferes with the accuracy of the 
perception. We have learned by experience to make certain per- 
ceptual reactions to certain stimuli ; but we have not learned, and 
at present cannot learn, to discriminate the subtle details corre- 
sponding to the essential points in these stimuli. 

The signs of character, like the signs of emotion, we know are 
physiological : they are primarily movements, not only of the facial 
muscles, but of the vocal muscles, and of the body generally. We 
estimate personal characteristics from the voice, the posture and 
walk, and the movements of the arms and hands, as well as from 
facial expressions. Secondarily, the effects of previous actions, in 
the lines of the face and the attitude of the body, perhaps a cer- 
tain characteristic of the voice, are important physiological traces. 
Anatomical characteristics, like hair and eye color, and the size 
and shape of organs such as the eye and ear, which are not af- 
fected by use, and the conformations on the bones of the head and 
face, have absolutely no known sign value, except as signs of ra- 
cial origin. If we were in any doubt on this point, the way in 
which most "successful" systems of character analysis contradict 
each other, by assigning quite different characteristics to the same 
anatomical detail, and the same characteristics to quite different 
detail, would be sufficiently conclusive as to the present meaning- 
lessness of such anatomical configurations. 



258 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

No system of character reading by physiological signs has been 
devised, and such a system can be devised, if at all, only throngh 
prolonged psychological and genetic investigation. Any scheme 
which might be constructed by the type of persons now exploit- 
ing " character analysis" would be an actual detriment, since at- 
tempts to use it would prevent the ' ' analyst ' ' from making use of 
the actual and undiscriminated physiological sign. The bogus 
anatomical systems, however, do not interfere. The "analyst," 
when he really makes an accurate reading, does it just as you or 
I would: through the physiological signs, to which he pays no 
attention: and then he finds in his anatomical system the details 
which confirm his judgment, ignoring those which do not. And 
it is quite possible for an ignorant person to be a faker in this 
way without being aware that he is faking. 

Another type of definite perception through imperceptible 
signs is that in which objects which are brought near a blind or 
blindfolded observer are recognized, or an object is recognized 
without the object being distinctly "sensed." In one experiment 
of this kind, 105 four frames, a foot square, were used. One was 
filled solid with wood, one with lattice work, one with wire net- 
ting, and the fourth was completely open. Three blindfold reac- 
tors discriminated these frames correctly, when brought near the 
face, in 90, 68 and 94 per cent of the cases respectively. 

In this experiment, the discrimination failed when the reactor's 
ears were stopped; indicating that the signs were really auditory, 
although not perceived as such. Variations in the reflection of 
sounds by the solid wood, lattice and netting, and absence of re- 
flection by the other frame, could conceivably supply different 
auditory patterns, provided incidental sounds were present to be 
modified. If conducted in a practically soundless place, the dis- 
crimination would therefore be expected to fail. However, other 
tests on different reactors have shown that discrimination of this 
sort is possible when the ears are stopped, thus raising the hypoth- 
esis that thermal signs may be effective (heat radiated to or 
from the object being the stimulus) or that air pressure, result- 

looMacDougall, American Journal of Psychology, Vol. XV, p. 387. 



THE DEVELOPMENT OF PEKCEPTION 259 

ing from the movement of the object as it is brought toward the 
face, is responsible 

In any case, the experiments clearly demonstrate perception 
through unperceived signs: in which one is conscious-, not of the 
data actually presented, but of its ' ' meaning. ' ' 

A somewhat similar case of symbolic perception has been found 
in experiments with the spatial illusion figure known as the Miiller- 
Lyer Figure. 106 In this figure, the short angular lines produce an 
appearance of inequality of the two parts of the line when they 
are actually equal. It has been found that the illusion may be 
produced when the short angular Hues are so faint as to be un- 
detectable by the reactor. Although imperceptible in themselves, 
they nevertheless change the total visual pattern measurably. In 
other trials, with different reactors, no effects may be produced. 
The faint stimuli evidently can be ignored. 



loeSee Chapter XIII, p. 296. 



CHAPTER XIII 
SPACE PERCEPTION 

§1. Space perception and muscular activity. 

Space is perceived through, all the senses, but by all except 
kinesthesis, it is perceived by means of signs. Vision and touch, 
the other most important space perceiving senses, can primarily 
perceive only extensity or bigness. Stimulation of more receptors 
in the retina or the skin results, in the perception of more of the 
sense data, in an extensity (not in intensity or durational) sense. 
Stimulation of different receptors gives perception of different 
sense data, but not primarily of the space difference. There is 
no conceivable way in which the perception of space could be 
built up except through muscular activity and resulting kines- 
thesis : and an inherited capacity to perceive space visually or 
factually is due to the inheritance of reaction to signs, such as 
might be built up otherwise through experience. 

Suppose that, vision being excluded, two spots on the skin of 
the arm are stimulated successively. If no tactual space signs 
have been built up, or inherited, these are felt as different 
touches, but not as in different places; and stimulation of a large 
number of spots gives no perception of distance or direction of 
these spots with reference to each other. But, if these spots are 
stimulated successively by moving the finger from one to the 
other: or if they are stimulated successively by some external 
object, through movements of the arm which bring the different 
spots successively in contact with the object, the tactual pattern 
becomes associated with the movements and the amount of move- 
ment, and so is woven gradually into a space pattern, in which 
distance and direction in space are involved. Distance and direc- 
tion are not kinesthetic sentienda themselves, but are relations, 
which, first experienced between kinesthetic sentienda, are subse- 
quently experienced between the tactual sentienda. A given tac- 
tual sentiendum, such as may be obtained from a certain spot on 
the skin, then becomes perceptible with space relation to other 

260 



SPACE PERCEPTION 261 

points on the skin, and so is perceived as on a definite part of the 
body. In some cases, the tactual datum is merely the sign of a 
position in space. 

The several positions of external objects in space, that is, 
their distances and directions from other objects, are perceived 
in the same way. A touch on the finger tip, followed by a touch 
on the same spot, with a definite arm movement entering, is the 
basis for the perception of the distance and direction of the second 
object from the first, assuming that the objects are not moving. 
The exclusion of motion of the object is achieved by repeating the 
exercises, and discovering whether the same amount and kind of 
movement is required for each trial. If under artificial condi- 
tions, an object is made to move from the one point to the other 
in the plane of the arm movement, an illusion of two objects in- 
stead of one is created, but the spatial positions may be correctly 
perceived nevertheless. 

The perception of extensities of data as spatial depends on the 
discrimination, within the area stimulated, of smaller areas, so 
located that a movement is required to stimulate first one and then 
another by the same object. This explains why spatial discrim- 
ination is more acute on those parts of the body, such as the 
finger tips, on which variation in locus of stimulation, by small 
movements, is most frequently procured. The discrimination of 
two points as two on the arm is apt to be less accurate than on 
the finger tips; but the accuracy of discrimination on the arm 
may be greatly increased by practice, in which parts close to- 
gether are successively stimulated by movements of the other 
hand holding a pointed instrument. Without the possibility of 
exploration of area in this way, by muscular activity, extensities 
in the skin would never have become spatial at all, but would be, 
like the extensities of audition (pitches), merely non-spatial char- 
acteristics. 

Similar considerations apply to vision. By movements of the 
eyes, and by movements of the hands and fingers, or by moving 
small objects held in the hand, the various stimuli can be brought 
upon different retinal receptor groups, and thus the space rela- 
tions of the movements are associated with the receptorial posi- 



262 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

tions. In this way the perception of lateral distance and direc- 
tion has been built up. 

The dependence of visual space upon muscular activity has 
been strikingly shown by experiments in which lenses worn in 
front of the eyes re-invert the field of vision. In normal vision, 
since the rays of light cross in the eye, the picture on the retina, 
which is the actual stimulus pattern, is inverted and reversed right 
and left. If you are looking at a man standing erect, in the image 
on your retina the man is "standing on his head," i. e., the head 
is down, the feet up; and the image of his hand at your right is 
on the left side of the retinal image. Yet you see the man as 
upright, and in actual position as regards right and left. This 
has seemed to some theorists difficult of explanation, yet it is quite 
intelligible as a function of muscular activity, in the light of the 
experiments of Stratton which we have just described. 

In these experiments, the reactor wore the lens combination 
for a number of days, removing it at night only, so that his vision, 
during the period of the experiment, was always with retinal 
images re-inverted in positions exactly opposite to those of 
normal vision. At first consequently space relations were seen 
reversed. An object really at the right was seen at the left, and 
vice versa, and all objects were seen inverted. Attempting to 
touch an object resulted first in a movement in the wrong direc- 
tion. In the course of days, however, the muscular activity set 
up new associations of retinal sign and space, so that the field of 
vision began to resume its normal position, and manipulation of 
objects approached normal. On final removal of the lenses the 
field of vision was confused, and required further time for read- 
justment to "normal' ' conditions of stimulation. It is obvious 
that vision alone gives no space relation, but that with any fixed 
correspondence of visual sign with external space, perception of 
the space relation may be built up. 

Another illustration of the building up of the space perception 
habit may be obtained by putting a prism in front of one eye, 
keeping the other closed ; or still better, by putting prisms in 
front of both eyes, the prisms having the bases in the same direc- 
tion. Objects are then seen displaced, in the direction opposite 
the bases of the prism : if the prisms are placed with bases to the 



SPACE PERCEPTION . 263 

right, an object is seen at the left of its true position. The visual 
pattern of the object, and the muscular pattern of the eye and 
head position, taken together, stimulate a reaction which will bring 
the hand, for example, to the point in space at which the object 
would normally be in order to produce that stimulus pattern. On 
account of the bending of the light rays by the prism, the object 
is at a point to the right of that at which, without the prism, it 
would produce the pattern. Hence, in trying to touch the object, 
the hand will be moved too far to the left. Practice quickly 
modifies the reaction, however, and at the end of a few minutes 
of muscular exploration of the field of vision, objects are seen 
"in their proper places:" that is, the new stimulus patterns pro- 
duce exactly the same reactions which the corresponding patterns, 
without the prism, produced. A more conventional and less ex- 
planatory statement is that, new associations between the visual 
signs and the space relations have been set up. 

In all these cases it is obvious that the visual stimulation alone 
does not constitute the effective stimulus pattern. A fixed point 
in the visual field may stimulate almost any group of retinal re- 
ceptors, according as the eyes are turned in their sockets ; as the 
head is turned on the shoulders, and according to the position of 
the body itself. In a given position of the trunk, and varying 
positions of the head and eyes, the same movement of the hand is 
required to touch a given object. The reaction terminating in the 
movement may be stimulated by a great many different patterns, 
involving a great many different positions of retinal stimulation, 
but in each of which a given retinal position is combined with 
specific positions of the eyeballs and of the head. It is certain, 
therefore, that the total pattern of visual and muscular stimula- 
tion (including stimulation of neck and eye muscles), is effective 
in directing the movement. A visual stimulation alone cannot 
produce an effective movement, since many different retinal stimu- 
lations correspond to the same movement, and each visual stimu- 
lation corresponds to a large number of movements. 

§2. Visual depth perception. 

Perception of depth, or distance from the eye, depends upon 
still more complex conditions of stimulation, and in these cases 
the effective data or stimulation conditions are, to a large extent, 



264 ELEMENTS Or SCIEXTIFIC PSYCHOLOGY 

signs : that is, are not perceived themselves, when the space rela- 
tions they "mean" are properly perceived. 

Accurate reaction to a stimulus pattern, and therefore accu- 
rate perception, depends upon the occurrence of patterns which 
correspond to the facts pereeiYed: and discrimination between two 
facts depends upon the existence of effectively different stimulus 
patterns for the facts discriminated. The differentiation in pat- 
tern corresponding to different distances of objects is due to 
several different peculiarities of retinal and mnscnlar function, 
which may be briefly listed as : (1) Convergence, (2) Accommoda- 
tion, (3) Parallax. (4) Binocular disparity, (5) Intervention, 
(6) Chiaroseura. (7) Linear perspective, (8) Angular perspective 
(9) Aerial perspective. (10) Foreshortening. These we will dis- 
cuss in detail. 

(1) Convergence: The two eyes normally work together as 
one organ. They are independently stimulated, but the reaction 
is the product of both, and although the stimulation is double, the 
object may be seen as single. This result is due to the existence 
of corresponding points on the retinae. 

If the visual stimulus for a point source falls on the center of 
one fovea, and at a certain point approximately at the center of 
the other fovea, the point is seen as single. These two retinal 
points are corresponding points, and the reaction and perception 
obtained from either are in many respects the same as may be 
obtained from both together. If, however, the stimulation falls 
on one foYea as before, but is made to fall at a slightly different 
point on the other ; which may be done experimentally by placing 
a prism before that eye, or pressing with the finger on the eyeball, 
the object is seen double. The stimuli are no longer on corre- 
sponding points. 

For every point on the retina of one eye, there is a correspond- 
ing p>oint on the retina of the other eye. This is the law of cor- 
responding points. Xormally, corresponding points are in the 
same relative anatomical position in each eye, although in some 
eyes there may be a deviation from this rule. In looking atten- 
tively at an object, the eyes tend to take the j)osition which will 
bring the image of each point in the object, so far as possible, on 
corresponding points of the retinae. In general the details most 



SPACE PERCEPTION 265 

attentively observed are brought (or their retinal images are 
brought) on the fovea. Obviously, for objects at different dis- 
tances, different positions of the two eyes will be required to 
bring a point in the object on corresponding points in the two 
retinae. This may be illustrated by a diagram, which the student 
should draw. In looking from a far object to a near object, when 
both are in the same line through a point midway between the 
observer's eyes, the eyes must move so that the corneae move 
towards each other. This movement is called convergence, and 
by extension the term is applied generally to the angular position 
of the eyes, with regard to each other. The movements of con- 
vergence, or the muscle stimuli patterns aroused by them, become 
parts of the total pattern effective in space perception. Objects 
seen with more convergence are seen as nearer than objects re- 
quiring less convergence because the reactor has uniformly found 
that less movement by the hands, or less locomotion, is required 
to reach the first object than is required to reach the second. 

Convergence, and the doubling of objects due to stimulation 
of non-corresponding points, may be illustrated by holding a pen- 
cil about IS inches before the eyes, with the point just below a 
mark on the Avail, at several feet distance. If one converges the 
eyes on the pencil point, the mark on the Avail may be seen double : 
if one coirverges on the mark, the pencil point is seen double. 
Ordinarily, these ''double images" are not consciously seen, be- 
cause they are signs of depth. It is important for our under- 
standing of the function of signs, to note that with both eyes open, 
with an object doubled by too near or too far convergence, one 
cannot directly distinguish betAveen the image of the right eye, 
and the image of the left. By closing and reopening one eye, one 
can discoA'er that with too near convergence, (/. <?., eomrergence 
on the pencil point Avhile observing the doubled mark on the Avail) 
the images are Jiomonymoiisly doubled: that is. the right eye's 
image is seen to the right of the left eye's: and that Avith too far 
coirvergeiice, the images are lieieronijmoushj doubled: that is. the 
right eye's image is seen as if at the left of the left eye's. But 
Avith both eyes open, it is impossible to distinguish directly be- 
tAveen homonymous and heteronymous images, although these are 
important signs of distance, the object homonymously doubled 



266 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

always being beyond the convergence point, and the heterony- 
mously doubled object being always nearer than the convergence 
point. Not only are these two sets of signs not distinguishable 
from each other as signs, in ordinary vision, but they are not even 
seen: that which is perceived is the distance or direction of which 
they are the signs. 

(2) Accommodation. The eye, like a camera, must be fo- 
cussed for different distances. Focussing, or accommodation, is 
accomplished by a change of shape (curvature) of the crystalline 
lens. The lens, in its supporting ligament or capsule, is flattened, 
when the eye is at rest, by the internal pressure of the eye. Con- 
traction of the ciliary muscle relaxes the tension on the capsule, 
and allows the lens to increase its thickness by its elasticity. The 
action of the ciliary muscle is perceptible, through the stimulation 
of the afferent neurons terminating in it. At short range, a slight 
change in distance of the object inspected necessitates a change 
of accommodation. For distances of over six meters from the eye, 
accommodation changes are slight, and beyond twelve meters are 
practically negligible, the "resting" condition of the lens being 
the approximate adjustment for all distances over that. The mus- 
cular stimulations resulting from accommodation are, therefore, 
signs of distance only at comparatively short range. 

Accommodation changes may be observed by a method similar 
to that described for convergence. The pencil point should be 
brought in line with a distant mark and one eye, the other eye 
being covered. Changing the fixation from the pencil point to the 
distant mark, or vice versa, entails muscular changes easily per- 
ceived after a little practice, and clearly localized within the eye 
balls. Movements of convergence of the covered eye will occur, in 
the change of accommodation, because convergence and accom- 
modation are habitually integrated, a definite degree of accommo- 
dation and of convergence being required for each distance. In 
ordinary vision, it is difficult to distinguish clearly the activity 
of accommodation from that of convergence, since the two are 
normally associated. But in the exercise described, the seeing eye 
being in line with the two observed points, makes no convergence 
movement, convergence being accomplished by the covered eye 



SPACE PERCEPTION 267 

only. Hence the accommodation movements of the eye may be 
observed. 

(3) Parallax. If you look at a wall or background of any 
kind holding the finger, or a pencil, at arm's length before the 
eyes and then move the head from side to side, the relative posi- 
tion of the ringer on the background, or its projection on the back- 
ground, changes as the head moves. The near object (finger) is 
apparently displaced in the direction opposite to that of the head 
movement; or the background is displaced in the direction of the 
head movement. The greater the distance between the finger and 
the background, the greater the apparent movement. This phe- 
nomenon of apparent relative movement of objects at different dis- 
tances, when the eye shifts its position laterally, is parallax. The 
direction of the parallactic movement is a sign which indicates 
which object is nearer, which farther: and the apparent magni- 
tude of the movement is a sign of the relative distances. 

(4) Binocular disparity. The consideration of parallax sug- 
gests at once that the two eyes, being at different points, will not 
receive the same stimulus pattern from a field of vision in which 
there is actual depth. Looking at a wall, with a pencil held at 
arm's length before the eyes, open the. eyes alternately, and you 
will notice that a sort of parallactic effect is obtained without 
head movement. The right eye will see the pencil at the left of a 
certain point on the wall : the left eye will see it at the right. This 
is closely connected with the homonymous and heteronymous 
doubling of images but is not the same thing. The result of this 
difference in point of view of the two eyes is disparity of the 
image on the two retinae. With convergence for a certain dis- 
tance, not only is there doubling of images for objects at a less or 
greater distance, but the relative spacing of details in the two 
retinae is different, and the amount of a far object covered or 
hidden by a near object may differ. 

The stereoscope takes advantage of the phenomenon of binocu- 
lar disparity by presenting a separate picture to each eye. The 
pictures are originally taken by a camera with two lenses, so that 
they together represent a scene just as it would be seen by the 
two eyes, or perhaps with the binocular difference slightly exag- 
gerated by placing the camera lenses a little farther apart than 



268 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

the normal interocular distance. These pictures are viewed through 
lenses, which are sometimes slightly prismatic in shape, so that 
the normal convergence for the apparent distance is permitted, 
and the two pictures blend into one view, in which depth effects 
are striking. The pictures can be combined, by a practical ob- 
server, without the lenses, but this is impossible for the untrained 
observer, since getting the pictures in the two eyes in correspond- 
ing positions requires, if no lenses are used, almost parallel direc- 
tion of the eyes, with which is associated accommodation for a 
great distance, instead of the short distance at which the pictures 
are seen. 107 

Another device for making use of binocular disparity in re- 
producing depth effects is the anaglyph. In this device, the pic- 
tures, taken originally with a stereoscopic camera, are printed 
superposed, or rather, with a certain detail in each superposed, 
the degree of superposition for other parts of the view varying 
with their depth from the superposed detail. The pictures are 
printed in complementary colors, e. g., red and green, and the 
observer is provided with spectacles in which one glass (or gela- 
tin film) is red, and the other green. The glass before the right 
eye must be of the color in which the picture intended for the 
right eye (taken with the right lens of the camera) is printed, 
the glass before the left eye of the color of the picture for that 
eye. Since the red picture cannot be seen through the green glass, 
and vice versa, each eye sees its proper picture, and the combina- 
tion gives depth as in the stereoscope. 

Various attempts, mostly foolish, have been made to introduce 
binocular disparity into the movies. It might be done by the 
anaglyph method by superposing a right eye and left eye picture 
in complementary colors on the screen, and giving each spectator 
a pair of spectacles of the same color. In addition to the expen- 
siveness of such a plan, so much would be lost in definiteness and 
illumination, and in the comfort of the spectators, that there would 
be a decided lessening of the effectiveness of the picture. The 
stereoscopic principle could be applied by projecting right-eye and 
left-eye pictures side by side from a double film, or from two 



10 7l n looking at a single picture, a better effect of depth is obtained by using one 
eye only, because of the lack of binocular disparity when both eyes are used. 



SPACE PERCEPTION 269 

synchronized films: fixing at each seat a binocular telescope 
through which the spectator would view the pair : but this would 
be still more expensive, and the gain through depth would not 
offset the other losses in the picture. 

A number of attempts have been made by projecting right 
and left eye pictures alternately on the screen. These attempts 
are due to ignorance of the principle of binocular disparity. In 
order to succeed, a double shutter before the eyes of each specta- 
tor would be needed, to expose the eyes alternately, in perfect 
synchronization with the film exposures, so that the right eye 
would see the right-eye picture only; the left eye, the left-eye pic- 
ture only. Without the shutters, the alternation merely produces 
messy pictures, unpleasantly blurred, or with a disagreeable mo- 
tion effect, 

The four signs of depth so far discussed cannot be simulated 
in ordinary pictures. The first and fourth are also binocular: 
they require the combined function of the two eyes. The signs 
yet to be described are all monocular, that is, they apply to one 
eye as well as to two: and they can be simulated or represented 
on a single flat surface, as in a picture or on a movie screen. 

(5) Intervention. In discussing binocular disparity we noted 
that one of the two stereoscopic pictures may show a far object 
less covered by a near object than the other. In a single picture, 
the mere partial covering of one object by another is a sign that 
the partially covered object is farther away than the covering 
one. If two men are seen, or are represented in a picture, both 
facing the spectator, with the outline of one completely shown, 
and only part of the outline of the other shown, the figure of the 
second man terminating at the outline of the first, the first is seen 
as in front of the second, although there may be no other sign 
of difference in depth, and although, in a picture, they are both 
painted on the same plane. A number of such interventions may 
be introduced into a picture, the first dog or tree or man partly 
occluding the second: the second partly occluding the third, and 
so on, thus giving " depth" to a scene which otherwise would ap- 
pear "flat." 

(6) Chiaroscuro, or the distribution of bright lights and 
shadows in an actual scene is dependent on the depth relation, 



270 



ELEMENTS OF SCIENTIFIC PSYCHOLOGY 



and the direction of illnmination. Crags, projecting from can- 
yon walls, cast shadows to the left, if the snn is on the right: to 
the right, if the snn is on the left. But the fact that they cast 
shadows at all is partial evidence that they project from the wall. 
More signs are needed, however, since caves or holes in the wall, 
of suitable shape, could appear as the same sorts of shadows, if 
the light were from the opposite direction. The decisive factor 
in this case, therefore, will be the high lights or areas of bright 




Fig. 19. — Shadows as signs of depth. The design may be seen either as a cameo illuminated 
from the right, or as an intaglio illuminated from the left. The stronger tendency is to see it in 
relief, because cameos are more frequently seen than are intaglios. There is in this figure nothing 
except the shadows to give it either appearance. 

illumination. In some cases it is impossible to tell whether a cer- 
tain shadow is in a depression, or is cast by a projection. A mis- 
take or false assumption as to the direction of illumination may 
produce a serious error. A bas relief, lighted from the side by a 
concealed source, 'may be mistaken for a cameo, if the direction 
from which the light comes is mistaken. 

(7) Linear perspective. The retinal image of an object varies 



SPACE PERCEPTION 



271 




272 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

in size inversely as the distance of an object from the eye. An 
ink bottle at twenty feet from the eye has a retinal image just 
half the diameter of the same object at ten feet. The difference 
in size of the retinal pattern may give rise to perception of dif- 
ferent sized objects, or to a perception of objects at different dis- 
tances, since a mere difference in the size of the image could corre- 
spond to either of these spatial differences. In any case, some 
other sign must cooperate. If there is some sign which tends to 
produce the perception of equal distances, the sizes are perceived 
as proportionate to the image sizes. If, however, there is a sign 
which indicates equal size, the distances are perceived as merely 
proportional to the image diameters. Men, for example, are as- 
sumed to be of approximately the same height, unless some special 
indication of shortness or tallness is evident. Hence, varying sizes 
of images are signs of varying distances. The width of a road, 
or of a long corridor, is assumed as constant. To represent such 
a road or corridor on a plane, as in a picture, the width of the 
road or corridor, as depicted, must decrease to mean increasing 
distance, because this is the retinal condition in actually viewing 
such a scene. This correspondence between increasing distance of 
object and decreasing size of retinal image is conventionally called 
Linear Perspective. 

(8) Angular perspective. An angle formed by two lines 
forms an image of a varying angle on the retina, according to 
the direction from which the angle is viewed.^ A right angle, for 
example, such as that formed by the edges of a table top, may 
have a retinal image varying from 180° to 0°, according to the 
direction from which the table is viewed. The image of the table 
top varies from a rectangle to straight line, through various rhom- 
boidal shapes. The depth of the table, relative to the eye, is per- 
ceived in large part in accordance with the sign. If seen as a rect- 
angle, both ends of the table must be equally distant from the 
eye: if seen as a rhomboid, one edge is farther away than an- 
other, and the more the rhomboid deviates from a rectangle, the 
greater the relative difference in depth. 

Angular perspective and linear perspective are equally impor- 
tant in drawings, giving definite depth impressions if the natural 



SPACE PERCEPTION 



273 



conditions are observed, and destroying depth effects if not in 
accordance with actual space conditions. 

(9) Foreshortening. When a table top is viewed from a posi- 
tion opposite the middle of one end, and slightly above, the image 
of the table shows linear perspective; the farther edge of the 
table being shorter than the near edge: it shows angular perspec- 
tive; the two nearer angles being less than 90°, the two farther 
angles being greater than 90° : and it also shows foreshortening; 



; 








Fig. 21. — Angular 



perspective, foreshortening and intervention. (Copyright, 
lishing Company. Republished by permission. ) 



1921, Life Pub- 



tlie length of the sides being shortened in proportion as the line 
of vision (line of regard) approaches the plane of the table top. 
The maximal length of these lines in the retinal image, for a given 
distance of the table from the eye, is obtained when the line of 
vision is perpendicular to the table top: the length approaching 
zero as the eye approaches the plane of the table. 

Foreshortening, as a sign of depth, depends, therefore, on other 
cooperating factors which indicate the relative length of the fore- 
shortened line, as compared with other linear distances in the 



274 



ELEMENTS OF SCIENTIFIC PSYCHOLOGY 







ill 









<U o 



.tJ o 



B.ti 



o t> 




SPACE PERCEPTION 



275 




<« o 

o *+* 

«!5 



o S 



bo 

•si 
1 3 



US 

S a 
o 

° s 



276 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

scene, and also indicate the distance of some part of the line from 
the eye. Lines of widely different length may have the same 
visual images, if the directions for the lines are properly chosen, 
and, conversely, the same line, in different directions, has vary- 
ing lengths in the visual image. In cases where no auxiliary signs 
are present, the depth relation perceived may be quite different 
from the actual depth relation. 

(10) Aerial perspective. The atmosphere usually carries dust, 
and sometimes water particles and smoke, which distort, disperse, 
or selectively absorb the rays of light, so that the outlines of dis- 
tant objects are blurred, and sometimes colored bluish or purplish. 
The more distant objects will be more blurred, and more colored; 
accordingly blurring of outline, and purple or bluish colors, are 
signs of distance. Painters make use of this fact, blurring and 
tinting the background, if intended to be seen at a considerable 
distance, and so giving the signs which would come from natural 
objects at such distance. In actual landscapes, illusory nearness 
of mountains is often produced when the air is unusually clear, 
and so the mountains are no more blurred and colored than much 
nearer objects would be under usual conditions. 

§3. Non-symbolic factors in space perception. 

The ten factors described above are signs in the technical 
sense of the term. In so far as these pattern details are perceived 
as such, the depth they ordinarily mean is not perceived, and con- 
versely, when the signs are unperceived, their depth meaning is 
most effectively perceived. For example: if two men, at differ- 
ent distances from the observer, are perceived as of different 
sizes, in accordance with the actual sizes of the visual images the 
observer has of them, the distances of the men are not accurately 
perceived: and the relative distances are most accurately per- 
ceived when the men are perceived as of equal size (assuming 
that they are approximately of the same size). Similar consid- 
erations hold for all ten of the signs of visual depth. 

Depth perception through signs is obviously not an inference: 
we do not (in usual cases) perceive the sign, and infer the dis- 
tance or direction from it. We do not perceive the sign at all. 
It is a detail, or group of details, in the stimulus pattern which 



SPACE PERCEPTION 277 

immediately causes the total reaction through which we perceive 
objects in certain space relations. The depth and other space re- 
lations are perceived as integral parts of the total visual content. 
Signs are not the only means of visual depth perception. Vari- 
ous details of the visual pattern may produce depth perception, 
as well as other sorts of space perception, while being perceived 
themselves, as part of the content. A face, seen full, against a 
uniform background, will be seen with the nose in relief and the 
eyes sunken, even when the lighting is such that no one of the 
ten signs of depth is present. Even the picture of a face, with 
none of the ten signs represented, may be seen as the picture of 
a face, and not as a flat diagram of a face. This is in accordance 
with the general principle of perception, as earlier described, by 
which the presentation of a part of the data of an object pro- 
duces the reaction for the total object. A reaction to a face, in- 
cluding its space relations, has been built up through muscular 
exploration, and hence the presentation of certain characteristic 
features of a face will produce the perceptual reaction for a face. 
In less technical language : the space relations of a face have been 
"associated" with the visible outline and details, and are per- 
ceived when these are perceived. 

§4. Auditory space perception. 

The only space relations of auditory data in themselves are 
the relations of pitch and timber, and these are not analyzed be- 
cause there is no muscular mechanism by which the pitch and 
timber of tones can be varied. Sounds, therefore, function in 
space perception only as signs or as associations of distance and 
direction of the sources of the sound. The sound of a violin is 
not heard as spatial, but is heard as coming from a violin at a 
certain distance, in a certain direction. The auditory pattern 
varies according to the distance or direction of the source, in pitch, 
timber and intensity. 

The pitch of the sound from a certain source is higher when 
the source is moving towards the ear, and lower when the source 
is moving away from the ear. This may most easily be noticed 
by comparing the pitch of a locomotive whistle when the train is 
rapidly approaching, with the pitch when the train is passing. 



278 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

Since sound waves travel through the air at approximately 1000 
feet per second, the pitch of the note, when the sonrce is ap- 
proaching, will be the normal pitch of the note multiplied by 1000, 
divided by the speed of the train in feet per second. In ordinary 
life, perceptions based on these pitch changes are not built up, 
and the only awareness of motion due to such pitch changes is 
due to inferences from the observed changes. 

The loudness (intensity) of a sound varies inversely as the 
square of the distance of the source. Hence, the nearer the source, 
the louder the sound, and if the normal loudness is known, an in- 
ference as to distance may be made. Since there is repeated ex- 
perience of objects sounded at various distances, perceptions of 
different distances are built up, but only with rough accuracy. 
A faintly sounding violin or human voice is experienced as at a 
greater distance than a loudly sounding violin or voice. Since 
the same loudness can actually come from different distances, ac- 
cording to the absolute sounding of the instrument, such percep- 
tions are subject to grave error. 

The relative loudness of sounds in the two ears varies with 
the direction of the sound with respect to the head. If the sound 
comes from the right, the right ear is more strongly stimulated 
than the left, on account of the " sound shadow" cast by the 
head. 108 If the sound comes from the left, the left ear is relatively 
more stimulated. Hence, the general direction from which sound 
comes is readily perceived, the difference in intensity being an 
unperceived sign. The intensity gives no sign as regards the 
direction of forward and back, up and down, since from any points 
in the median plane, the intensity effect on the two ears is equal: 
hence, a sound directly in front of the observer may be heard as 
above, or behind, unless other signs or associations are present. 
Variation in the position of the sound from the position directly 
opposite one ear towards the medial plane varies the relative in- 
tensities in the two ears; but variations forward, back, up and 
down produce the same effects, and hence it is impossible, by the 
intensity signs alone, to distinguish sounds coming from positions 
diagonally upward, downward, back, or forward. For example: 

losinterferenee of waves transmitted through the head from one ear to the other 
may also affect the relative intensity in the two ears. 



SPACE PERCEPTION 



279 



the position of a source of a pure tone directly opposite one ear 
is correctly perceived; the position of such a source 10 degrees 
forward from this point is perceived correctly as far as its angle 
is concerned, but it may be perceived as 10 degrees up, down or 
back, instead of forward. 

The tact that the intensity differences in the two ears are only 
signs, and are not perceived themselves, may be demonstrated by 
employing two sources, of the same pitch and timber, one oppo- 
site each ear of a blindfolded reactor. Two telephone receivers, 
actuated by a common current, are adequate. The reactor hears 
only one sound, and if the sources are made of unequal intensity, 
the sound is heard as coming from a source on the side of the 
higher intensity. By finding the relative intensities of the two 
sounds which cause the reactor to localize the sound in his median 
plane, the relative sensitivity of his two ears may be noted. 

Discrimination of positions forward, back, up and down, are 
possible in audition only through timber signs. The concha of the 
ear selectively modifies the partial tones in a complex note so 
that the timber is not quite the same in these different positions 
of the source. Obviously, perception based on this sign is possi- 
ble only when the sound employed is a complex and familiar one. 
In case of a pure tone, such localization is impossible. 

On the whole, auditory space perception is vague and inac- 
curate. Most of our localizations of sources of sound are based, 
not on auditory, but on visual or other signs of associations. Even 
the binaural signs may be inefficacious when visual associations 
are against them. If a violin is silently bowed at the reactor's 
right, in his field of vision, and a concealed violin is actually 
sounded on the reactor's left, he will perceive the sound as com- 
ing from the wrong direction, in spite of the fact that the binau- 
ral sign of relatively higher intensity in the left ear is present. 
The success of the ventriloquist is largely due to this sort of over- 
coming of auditory conditions by visual ones. Such control of 
the voice as the ventriloquist uses is confined to changes in tim- 
ber, which make the voice unnatural in sound. Since the tones do 
not sound like those ordinarily coming from a human throat, we 
are more easily disposed to perceive them as coming from the 



280 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

object from which the ventriloquist, by visual cues, or verbal de- 
scription, makes us perceive them to come. 

§5. Space perception through other senses. 

Although odors are conveyed to the nasal receptors from dis- 
tant objects, there is no olfactory perception of direction, and 
little of distance. There are neither signs nor associations of 
direction in olfactory perception, since the air-dissolved odorous 
particles must enter the nostrils in the same way, and make the 
same impression on the receptors, whatever the direction from 
which they come to the external nares. There is no muscular 
mechanism which varies the adjustment of the olfactory appa- 
ratus for either distance or direction. The perception of direc- 
tion of an odorous object is always tactual, thermal, auditory, or 
visual, or a combination of these. An odor of honeysuckle, when 
the wind is from the left, may cause the perception of "honey- 
suckle at the left : ' ' but the signs are the tactual or thermal stimu- 
lations, the breeze ? or the visible movement of smoke, leaves, or 
other indications of air currents. If the honeysuckle is smelled, 
and also seen, the localization of the source of odor is visual. If 
we experience the characteristic odor of a wet dog in a dark 
room, the source cannot be localized until one touches the dog, or 
hears him. 

The relative intensity of an odor may be a sign of distance. 
The odor of any given source, at a given time, and in a given 
direction, is stronger when the object is near, and weaker when 
it is farther away. Hence, there are roughly valid olfactory per- 
ceptions of distance. No great accuracy is possible, however, 
since the odors of most sources vary from time to time, and the 
direction of air currents and the temperature and moisture of the 
air cause large variations in the odor from a given object at a 
given distance. The odor of a bed of petunias, at a certain dis- 
tance, may be faintly perceptible at one time, and may be strong 
at another. 

The qualitative character of certain odors varies with the in- 
tensity of the total odor, the odor being characteristically differ- 
ent at different intensities. In this respect, these odors behave 
as if they were made up of a number of elementary odors, the 



SPACE PERCEPTION 281 

relative intensities of the elements not varying in the same meas- 
ure, so that at one intensity, certain elements predominate, while 
at other intensities, other elements predominate. It may be that 
such changes, which occur with intensity change due to distance 
change, are changes in signs which might assist in the perception 
of distance. 

Gustatory localization could, in any case, be no more then per- 
ceived position of stimulation on the tongue. How far such 
localization is possible has not been determined. In the usual 
cases of gustatory perception, tactual data are also present, and 
are the bases of localization. Gustatory extensities are discrimi- 
nable, according to the area stimulated on the tongue. No dis- 
tinctions of olfactory extensities have been noticed. 

Organic sentienda have volume, or extensity, and are more or 
less accurately localized in the organism. Pains and aches, for 
example, may be "fine" or "sharp," or may be "massive," or 
extensive. Pains in the external muscles, and in the teeth and 
bones, are fairly well localized; and various cutaneous and sub- 
cutaneous sentienda: itches, pains, tickle, etc.: are localized ap- 
proximately. Sense data for the viscera, however, are very 
vaguely localized. Many persons cannot distinctly perceive hun- 
ger as in the region of the stomach, and for some the fullness of 
the bladder is referred to the abdomen generally. These facts 
agree with the general principle that exploratory muscular activ- 
ity is necessary in order to learn to perceive space location, and 
where such exploration is not fully possible, as is the case with 
the viscera, localization is imperfect. By movements of the trunk 
muscles, certain grossly defined variations in pressure on the vis- 
cera are possible, and hence a certain perception of space is built 
up. Pressure in the bladder is localized in the abdomen, because 
pressure on the abdomen from outside, or exercised by the dia- 
phragm or by the abdominal muscles, modifies the bladder pres- 
sure; and fine localization is impossible, because no fine explora- 
tory movements are possible. 

Certain painful feelings which are really in the viscera are 
perceived as located in areas of the skin. These feelings are 
"soreness" or "tenderness" due to diseased conditions of the 
viscera, and are known as "referred pains." Pains from specific 



282 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

portions of the alimentary canal and other visceral organs are 
referred to specific areas of the skin, and these " areas of referred 
pain" have been carefully mapped by Head and others. The 
"'referring" of pain in this way is apparently due to a synaptic 
connection between the afferent neural route from the skin and 
the afferent route from the viscera established somewhere along 
the line, perhaps in the spinal ganglia or spinal cord, so that cur- 
rent coming from the viscera reaches the cerebrum by routes over 
which current normally comes from the skin. The fact that the 
reference occurs, indicates that the transference of current is not 
normal, but is due to pathological conditions, for which no space 
perception system has been built up by normal life. The false 
localization would undoubtedly disappear in the course of time, 
but slowly, since muscular means for the quick referring of vis- 
ceral space perception are not at hand. 

§6. The perception of movement. 

The perception of movement is closely related to the percep- 
tion of space in two ways. In the first place, it is the original 
basis of all our space perception, and, in the second place, move- 
ment includes space as well as time. 

Movement of a part of the body in many cases functions as a 
sign, and not as an associate of spatial factors in perceived ob- 
jects. That is, we perceive the space relation, but not the move- 
ments which are essential to the perception. This is the case, 
for example, with convergence movements of the eyes, and in 
other instances where movement functions as a highly developed 
perceptual reaction. In the building up of these reactions, how- 
ever, movements function as associates: that is, as perceived de- 
tails upon which the indirectly perceived content depends. The 
relegation of associates to the position of signs, that is: from the 
conscious to the non-conscious level, is but one case of the general 
course of reactions, which -tend wholly, or in part, to become un- 
conscious in so far as they are completely perfected, the conscious 
factor being apparently important during the learning process, or 
where the reactions must be held constantly subject to modifica- 
tion. 

In many cases we find that movement of a body-part functions 



SPACE PERCEPTION 283 

as an associate, and not as a sign. If, for example, yon are blind- 
folded, and asked to compare the length of two sticks by "feeling' ' 
them, i. e.\ by moving the finger tips along them; the movements 
are perceived as movements, and at the same time are the basis 
for the space perceptions: they are part of the direct content in 
the total perception, in which the space relations are the indirect 
content. 

Movements of parts of the body with reference to the total 
organism,' are perceived through muscle receptors, tendon recep- 
tors, and joint receptors. In active movements, muscular contrac- 
tion and relaxation occur; the pressure and tension changes in 
muscles and tendons stimulate the receptors terminating there; 
and the movement of joint surfaces over each other stimulates re- 
ceptors terminating in the joint capsule and the cartilaginous sur- 
face of the joint. 

In movements of the head, in addition to the effects in neck 
and shoulder muscles, and the vertebral articulations, the recep- 
tors terminating in the semicircular canals are stimulated. Al- 
though the stimulation of the receptors in ordinary movements 
does not contribute directly to the perception of movement, that 
is, there are no sentienda connected with the stimulation of these 
receptors, it modifies the perception indirectly, since the reflex 
discharges initiated in these receptors modify the ensuing mus- 
cular activity, and hence modify the perceptions. The mechan- 
isms in the ampullae of the semicircular canals are not sense 
organs for motion: they are really receptor-organs for uncon- 
scious reactions affecting the muscular system in such ways 
as to assist in the coordination of movements, especially the move- 
ments of the eyes. 

Movements of the body as a whole, either rotation or transla- 
tion, are perceptible without the aid of vision, but only during, 
and for a short time after, acceleration or retardation. If a re- 
actor, blindfolded, is seated in a rotation chair, and the chair set 
in rotation, continuing thereafter to rotate steadily, without fur- 
ther acceleration or retardation, the reactor perceives the com- 
mencing of the rotation, and perceives himself as continuing to 
rotate for a brief time, usually from ten to fifty seconds, depend- 
ing upon the reactor, and the rate and amount of acceleration. 



284 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

Then, if the rotation is quite steady, he seems to come to rest, 
and to remain at rest as long as the rotation is steady. If the 
rotation be then stopped, the reactor feels himself stopping, and 
then for a number of seconds, rotating in the opposite direction, 
although really at rest. 

The acceleration stimulates the organism in various ways. 
The inertia of the body, if the reactor is supported only by the 
chair seat, causes a twisting of the body, which stimulates vari- 
ous kinesthetic receptors. The inertia also exerts a lateral strain 
in the skin and subcutaneous tissues of the buttocks and legs. 
The inertia of the viscera also causes changes in internal pres- 
sure, of the viscera against the thoracic and abdominal walls, and 
of the viscera against each other, and change in tenseness of the 
mesenteries. All these are efficacious in initiating the perception 
of rotation, and function as long as the acceleration continues, 
and while the normal tensions and pressures are being restored. 
When a reactor is set in rotation at a rate of one turn in two 
seconds, with acceleration from rest to full velocity in two turns, 
the visceral stimulation has been demonstrated to be a powerful 
one, from which alone definite perception of rotation would arise. 

In the process of acceleration, the semicircular canal receptors 
are stimulated. While this does not in itself give rise to a per- 
ception of rotation, it produces certain important muscular effects, 
chief among which are: (1) Increased tension of the muscles in 
resisting the torsion of the body above described: the torsion re- 
sulting from the movement impressed on the hips by the chair, 
and the inertia of the trunk and limbs. (3) Kelatively increased 
tension of the recti muscles of the eyes, on the side opposite the 
direction of rotation, causing the eyes to be turned in that direc- 
tion; that is, to lag behind. The lagging sets up a reflex which 
jerks the eyes ahead, and the lagging commences again. This 
alternate lagging, or drifting of the eyes in one direction, with 
the recovery or jerking in the opposite direction, is called nystag- 
mus. These muscular effects of simicircular canal stimulation un- 
doubtedly affect the perception of rotation: but their most char- 
acteristic results are produced after acceleration has ceased, that 
is, after the rotation has reached a constant speed. The nystag- 
mus, and undoubtedly the other muscular effects, persist after the 



SPACE PERCEPTION 285 

acceleration, which is the only stimulus, has ceased, and are the 
causes of the prolongation of the perception of rotation. This is 
evident from the fact that the perception of rotation normally 
ceases when the nystagmus ceases. If we wait until the effects 

RIGHT HORIZONTAL NY5TAGMU5 

Acceleration Clockwise 
Retardation Counterclockwise 



%> 






/ ":---~----""~V 



S- -^ 



^>. 






Reactors \\ \ 4tf^ *£FS3 / 7 Reactors 



Ridht \* "~* ~ * Left 




\\ 



i Clockwise Couriterciockwise 



/ 






Arrows under eyes indicate direction of slow "compensatory "" 
movement or "drift" Quick "saccadic" or "nystagmic" move 
ment is in opposite direction . 

Fig. 24. — Direction of eye movements in horizontal nystagmus. 



286 ELEMENTS OP SCIENTIFIC PSYCHOLOGY 

of the stimulation of the simicircnlar canal receptors have worn 
off (the stimulus itself having ceased with, or shortly after, the 
end of the acceleration) and then stop the rotation, similar ef- 
fects are produced, but in a reversed direction. The eyes drift 
in the direction of the preceding rotation, and are jerked back: 
and the body torsions, and tensions or lurch in limb muscles are 
the reverse of those found during and immediately following ac- 
celeration. The reactor has the "illusion of rotation" in the op- 
posite direction, which, in the normal subject, lasts exactly as long 
as the nystagmus does. If the rate of retardation in stopping is ex- 
actly the same as the rate of acceleration in starting, the nystag- 
mus and illusion of rotation in the one case lasts exactly as long 
as the nystagmus and perception of movement in the other: pro- 
vided, of course, that the rotation was continued long enough to 
allow the effects of the acceleration to disappear. 

Such stimulation is pathological, of course. In normal living 
conditions, rotations are brief, of relatively few degrees, and the 
retardation stimulus occurs so soon after the acceleration stimulus 
that the one practically cancels the other, and hence there are 
negligible after-effects. The condition of long continued rotation 
is one to which the organism has had no chance to adapt itself. 
Dancers and acrobats who practice long continued whirling or 
turning, gradually become adapted to the condition of stimula- 
tion, and lose the nystagmic and other objectionable effects. By 
brief periods of daily rotation in a chair, a normal subject will, 
in a few weeks, completely lose the nystagmic and other mus- 
cular effects of excessive semicircular canal stimulation, while re- 
taining full normal reaction to normal rotary stimulation. 

In addition to the effects of labyrinthine stimulation on the 
striped muscles, there are effects on the stomach muscles and prob- 
ably on other smooth muscles; and there is also an effect to which 
the terms dizziness and vertigo are sometimes applied. Since 
these terms also apply to the illusion of rotation following rota- 
tion, a new term ought to be applied to the sentiendum or sense 
complex in question, which is quite distinct from the illusion of 
movement. The illusion of movement, conversely, often occurs 
without this sort of "dizziness." 



SPACE PERCEPTION 287 

The effect on the stomach muscles is apparent as nausea, and 
when violent, as retching movements. Even when no distinct 
nausea is produced, changes in the normal stomach contractions 
are produced. 

In movements of translation of the body, that is: in motion 
on a straight line, the semicircular canals are apparently not 
stimulated. The receptors in the vestibule of the ear may, how- 
ever, be stimulated, and visceral, cutaneous and somatic stimula- 
tions occur under the influence of inertia, giving rise to the 
perception of motion. In this case, however, the perception of move- 
ment ceases very shortly after acceleration ceases (provided that 
visual and auditory signs are excluded). The phenomena are most 
easily studied in an elevator, in which the visceral sense data, the 
tactual change in the soles of the feet, and the effects on the joints 
of the legs are readily brought under observation. 

§7. Equilibration. 

The maintainance of balance, as regards the force of gravity, 
is the result of reactions or modifications of reactions originating 
in the receptors of vision, the dermal and kinesthetic receptors, 
and the receptors of the vestibule of the ear. The importance of 
visual signs can be demonstrated by blindfolding a reactor, and 
causing him to stand upon a platform which can be tilted in vari- 
ous directions: the deck of a rolling ship, for example. In such 
a condition, equilibration is more difficult, and less successful than 
with the eyes open. Even in standing on a solid floor, the reac- 
toi cannot stand so nearly still when blindfolded as with his eyes 
open. The functions of dermal and kinesthetic factors can be 
readily observed by the blindfolded reactor himself when on an 
unstable platform. 

The vestibular mechanism has an important function on eqi- 
libration, through its effects on the striped muscles. If one starts 
to fall in a given direction, the stimulation of the vestibular re- 
ceptors seems to produce by reflexes increased tension on the 
muscles on the other side, facilitating the movements of recovery 
of balance. Whether the semicircular canal mechanism has any 
function in equilibration, is uncertain. 



288 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

§8. Visual anesthesia and perception. 

The eyes perform movements of two types, already described 
in the discussion of nystagmus. One type of movement is the 
drifting movement, characteristic of the observation of a steadily 
moving object, and of the slow movement in nystagmus. If you 
watch a white spot on a slowly revolving disc, or watch the bob 
of a slowly swinging pendulum, the eyes move so that for a con- 
siderable part of the path of the moving object, the image re- 
mains practically on the same portion of the retina, and is con- 
tinually seen. The other type of movement is characteristic of 
voluntary shifting of the eyes. If you look at an object directly 
in front of you, and then look at an object at the right or left, 
the eyes execute a quick movement from the first position to the 
second. The quick or "recovery" movement in nystagmus is of 
this type, and although not strictly voluntary, it is often desig- 
nated as such. In order to avoid confusion, eye movements of 
this type are now called saccadic. 

During the greater part of a saccadic eye movement, the eye 
is blind. This has been experimentally proved, and might be in- 
ferred from a variety of visual phenomena. This blindness pre- 
vents the blurring of the visual field, as the eyes are moved from 
point to point. If you keep the eyes fixed, and move an object 
in front of them, its outlines blur. A common illustration of this 
is obtained at night by waving a stick on the end of which a live 
coal has been fixed. The image of the coal is drawn out into a 
line of fire. But, if the coal is held at rest, and the eyes moved 
from point to point voluntarily, no such effect is produced. Oc- 
casionally the drifting movement of the eye can be obtained un- 
der such circumstances, and then a streak of light is seen: but 
this is an exceptional occurrence. 

If it were not for the anopsia during saccadic movements, the 
blurring of the field of vision in glancing here and there very 
probably would be not only disagreeable but disturbing to the 
efficiency of vision. In reading, the eye executes a series of sac- 
cadic movements from point to point on the printed line, and from 
the end of one line to the beginning of the next. One can easily 
imagine the confusion which would occur if the words were vis- 
ible during these movements. 



SPACE PEECEPTION 289 

The conditions of vision during saccadic eye movement of 
vertical and rotary types are at present obscure. We cannot say 
that there is regularly, if ever, anopsia during either of these 
types of saccadic movement. The results of observations during 
rotary nystagmus bear on this point. 

In horizontal nystagmus, which is readily obtained by rotat- 
ing the reactor for some seconds about the normal vertical axis 
of the head, the intermittent anopsia produces illusion of move- 
ment of the visual field, if the eyes are open, in the direction of 
the saccadic movements. During the slow, or drifting movement 
of the horizontal nystagmus, the eye sees, and the movement of 
the images across the retina cause the illusory perception of move- 
ment of the objects seen. During the saccadic recovery move- 
ment, the eye is anopsic, hence there is no reversed illusory move- 
ment. If the eye could see during both movements, there would 
be slow apparent movement of the field in one direction, alter- 
nating with rapid movement in the opposite direction. 

In rotary nystagmus, which may be obtained by rotating the 
reactor, seated, with head bent forward so that the normal ver- 
tical axis of the head is horizontal, the eye is rotated on its dorsi- 
ventral axis by the action of the oblique muscles. The rotations 
are alternately of the slow or drift type, in one direction, and the 
quick or saccadic in the opposite direction. If the eyes are open, 
the visual field appears to rotate like a wheel, either in the direc- 
tion of the slow or of the quick movement. Some reactors ob- 
tain the one illusion, others the other illusion, and some obtain 
both at different times. This would suggest that anopsia may 
occur during either type of rotary movement. 

Since with the usual type of eye movements in observing a 
scene, or in reading, repeated moments of anopsia occur, it is 
obvious that although the objects are seen continuously, the af- 
ferent current from the eye is intermittent. Conversely, if the 
scene is presented intermittently, as on the movie screen, at a 
sufficiently rapid rate, it is seen as continuous. Even if the rate 
is so slow that flicker occurs, there will be apparent continuity. 
If an actually moving object is being observed, it can be clearly 
seen in one of two ways. First, the eye may "follow" the ob- 



290 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

ject: that is, the eye may execute a drifting type of movement, 
at the same angular rate as that at which the object is moving, 
so that the image of the object is, for a fraction of a second at 
least, maintained at rest on the retina. This is the cause of the 
occasional distinct vision of the spokes of a rapidly turning wheel, 
which blur most of the time. If one casually observes the wheels 
of passing automobiles, one finds that the spokes at the top, or 
at the bottom, will " flash out" momentarily, according to the 
speed of: the eye movement. Spokes are never seen at the top 
and bottom both; and since the top of the wheel is moving for- 
ward faster than the bottom, a more rapid drift movement is re- 
quired to see the top spokes than is required to see the bottom 
spokes. If one observes a disc, rotated on a spindle, and having 
radial stripes or sectors of black and white, one finds that hori- 
zontal eye movement in one direction causes the stripes or sec- 
tors to appear at the lower part of the disc: eye movement in the 
other direction causing the stripes or sectors to appear on the 
upper part of the disc: because in this case the top and bottom 
of the disc are really moving in opposite directions. 

If objects are moving in various directions in the field of vision, 
as is the case of a man moving about, clear vision can be obtained 
only by a series of saccadic movements, introducing momentary 
periods of anopsia, so that the visual mechanism is stimulated 
intermittently. In these cases the moving objects are really pre- 
sented in a series of positions, not, in continuous movement, but 
are seen moving. This condition of stimulation is employed in the 
motion picture, the objects in action being presented in a series 
of positions, and hence seen as in motion, although the eye may 
be at rest. The intermittent nature of the stimulation in motion 
pictures may be clearly observed if the eye is allowed to drift, 
while a non-moving object (as the words of a title) is on the 
scene. Drifting of the eye brings the successive stimulations in 
different retinal areas, and therefore the words are seen multi- 
plexly. 

The so-called^ stroboscopic phenomenon is obtained when the 
eye is stimulated intermittently by a series of objects so nearly 
alike as to be indistinguishable. In the case of the striped or 
sectored disc, for example, if the stripes or sectors are uniform, 



SPACE PEKCEPTION 291 

that is, the white stripes or sectors all alike and equally spaced, 
and hence the black stripes or sectors also alike and equally 
spaced, and if the disc be illuminated by intermittent light so 
timed that the period between successive illuminations is exactly 
that required for a given white stripe to move to the position of 
the next white stripe, the disc will be seen as at rest. If the disc, 
for example, has twenty white stripes on a black ground, and is 
rotated once per second, it must be illuminated by intermittent 
light of twenty flashes per second in order to seem at rest. If 
the period of the intermittent light is slightly greater, the disc 
will seem to rotate slowly in its true direction: if the period of 
intermittence is slightly less, the disc will seem to rotate slowly 
backward. This explains the curious effect sometimes observed 
in the movies, in which a rapidly moving automobile has its wheels 
apparently not turning, or turning very slowly in either direc- 
tion. 

An illusion of movement in which the observer of a moving 
object seems to move, and the actually moving object to be at 
rest, is often observed in railway stations. A train next to the 
one in which the observer is seated begins to move, but seems to 
be at rest, while the observer seems to move in the opposite direc- 
tion. This illusion is due solely to eye movements. The moving 
of the train evokes repeated drifting movement of the eyes, with 
alternating saccadic recovery movements, exactly the sort of eye 
movements produced by watching a scene through which one is 
moving backwards. If the eye movements are inhibited, the illu- 
sion ceases: but the inhibition is sometimes very difficult. The 
same nystagmic movements which make an object at rest seem to 
move, make an object really moving in the opposite direction, at 
the same rate, seem at rest. The same sort of effect is produced 
when the observer is blindfolded, or in the dark, so that nothing 
is seen during nystagmus: the observer seems to rotate in the 
direction opposite to that in which objects, if seen, would appear 
to move. 

§9. Spatial illusions. 

Certain phenomena of space perception are commonly classed 
as spatial illusions, although the distinction between these phe- 



292 



ELEMENTS OF SCIENTIFIC PSYCHOLOGY 



nomena and the general phenomena of space perception is not 
sharp. Some of these illusions are easily explained on the funda- 
mental principle of habit, and the others are undoubtedly explic- 
able on the same basis. Many of them are named from the persons 
who first described them. 

(a) Aristotle's illusion. If two adjacent fingers are crossed, 
far enough to form a distinct crotch, and an object, such as a 
pencil, pressed into the crotch, the eyes being closed, the object 
is perceived distinctly doubled. If the tip of the tongue is pressed 



\ 



\ 



Fig. 25. — Poggendorf's figure. The two oblique lines are really segments of the same straight line. 



in the crotch, the tongue is perceived as forked. This perception 
is obviously the habitual one for the stimulus, since the opposite 
sides of the fingers are stimulated, which is the accustomed stim- 
ulus of two different objects. The perception of two objects has 
been built up as a response to this stimulus pattern, and results 
in the habitual way. It is true that the total stimulus pattern is 
different in the two cases: in the normal case the fingers are side 
by side: in the illusion they are crossed. The crossed position 
is distinctly perceptible in itself, hence it is possible to build two 
different reactions on the same pattern : a reaction of perceiving 



SPACE PERCEPTION 



293 



two objects from the tactual stimulation of the outer surface of 
the fingers when they are not crossed; and a reaction of perceiv- 
ing one object when the same tactual stimulation occurs with 
finsrers crossed. But the latter pattern of stimulation has occurred 



//. NS / 



« 



NS 



II 



%. 



\ 



Fig. 26. — Zollner's figure. The long lines are really parallel. 

so seldom in the experience of most persons that the reaction has 
not been built up, and the important "fingers crossed" part of 
the pattern is simply "disregarded:" that is, like a purely adven- 
titious detail of stimulation, it does not prevent the accustomed 
reaction from occurring. 



294 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

(b) Stratton's illusion. A converse form of the Aristotle illu- 
sion may be obtained when the two fingers are crossed, by stim- 
ulating simultaneously the two skin areas, one on each finger, 
which are habitually stimulated by a single object between the 
finger in the normal position. This illusion can sometimes be ob- 
tained when the fingers are not crossed, but are widely separated. 
In general, such stimulation gives rise to the perception of a broad 
object, of width corresponding to the separation of the fingers. 




Fig. 27. — Reversible perspective figures. At any moment the chair may appear either as 
viewed from the front or the rear. The other design, "Necker's Cube", will appear likewise in 
either of two positions. 

Stimulation by objects of different breadth between the fingers 
has been a common experience for most persons, and differentiated 
perceptions based on the total pattern of the tactual stimulation 
and the separation of the fingers (kinesthetic) have been built up. 
(c) Illusions of direction. The Poggendorf figure (Fig. 25) 
and the Zollner figure (Fig. 26) are typical illusion figures in 
which the relative direction of lines are distorted. In the Poggen- 
dorf figure, the two short lines, which are really on the same 
straight line, seem to be displaced, so that their prolongations 



SPACE PERCEPTION 



295 



would be not common, but parallel. The effect is the same as that 
which would occur if the points of intersection of the diagonal 
lines with the vertical parallel lines were kept the same, and the 
acute angles Avere made slightly more obtuse, while the vertical 
lines remain parallel. 

In the Zollner figure, the long lines, really parallel, seem to 
converge. In this case, also, the effect is as if the acute angles 
were rendered more obtuse, but the effect is on the apparent posi- 
tions of the long lines, and not the short ones. No satisfactory 





Fig. 28. — Jastrow's figure. The two outline figures are exactly alike. 



explanation of the building up of these perceptions has yet been 
given, although many theories have been advanced. 

(d) Illusions of angular perspective. Certain linear figures 
which constitute outlines of objects having depth, or difference 
in distance from the eye, may be so drawn as to be seen in either 
of two contrasting positions, the relatively nearer points in the 
one position being the farther in the other. Such figures (Fig. 
27) must be so drawn that there is no true linear perspective, 
and so that angular perspective and foreshortening are either ab- 



296 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

sent or equivocal: that is, are appropriate to both positions. In 
such cases, the stimulus-pattern is as near the habitual pattern 
for perception of the one position as the other. 

Such reversible perspective figures usually present the strik- 
ing phenomenon of fluctuation: on gazing steadily at the figure, 






Fig. 29. — Muller-Lyer's figure. The long line is divided into halves by the vertex of the 

middle angle. 

it appears for a time in one perspective, and then suddenly changes 
into the other. Tn some cases this change is due to ideational 
processes: to thinking about the other position. In other cases, 
the change occurs in an automatic way, with no preceding thought 




Fig. 30. — Dunlap's figure. Circle with apparently unequal diameters. 

of the second position. No verifiable explanation for this alterna- 
tion in reaction has been offered. 

(e) Illusions of area. Contrast effects of area and linear ex- 
tent are common. A given area appears larger when adjacent to 
a small area than when adjacent to a large one. A line, beside 



SPACE PERCEPTION 297 

a shorter one sometimes appears longer than it does when beside 
a longer line. In the Jastrow illusion (Fig. 28) two equal and 
exactly similar areas appear unequal because the adjacent lines 
of the two are unequal. In the Miiller-Lyer illusion (Fig. 29), 
which is the converse of the Jastrow illusion, two equal lines ap- 
pear of unequal length, because they are important diameters of 
unequal areas. In a third illusion (Fig. 30) (first described by 
the author), the effect of the unequal area on the equal lines car- 
ries over a third step, and makes a circle appear distorted. 



CHAPTER XIV 

THE THINKING PROCESS 

§1. The thought reaction. 

We know that there are two ways of being conscious of ob- 
jects, which we distinguish as perceiving and thinking: or, ab- 
stractly, as perception and thought. The attempt to define these 
terms leads to mere circumlocutions, but the processes to which 
they refer can be pointed out in concrete experiences. I perceive 
the vase of roses now on the table before me, in full daylight. An 
hour from now, when I am in another room, I may think of them : 
in this particular case, I may imagine them. The different types 
of thought — imagination, memory, conception — have been dis- 
cussed already in Chapter VIII. 

For the detailed understanding of thought; for the analysis 
of the conditions under which it occurs, and the ascertaining of 
its laws, it is necessary to reduce it to a psychobiological basis, 
just as has been done for perception. The empirical similarities 
between thought and perception, and the dependence of the sec- 
ond upon the first, as already discussed, indicate that the basis 
of the two processes is essentially the same: that thought, like 
perception, is intrinsically a reaction. The principle of parsimony, 
moreover, would necessitate our considering this hypothesis, and 
determining how far it fits the known facts and promotes further 
investigation. 

Reaction involves stimulation. Every reaction begins in the 
activity of receptors, which must be stimulated in some definite 
way. We must seek in the body therefore, for the neural mechan- 
ism capable of sustaining a thought reaction, and seek for the 
probable stimulus. At the outset, we must exclude the receptors 
of the so-called special senses: vision, audition, gustation, olfac- 
tion, and the dermal senses. In the first place, the functioning 
of these initiates perception: in the second place, thought, even 
thought of objects which appeal perceptually to these senses, may 

298 



THE THINKING PROCESS 299 

proceed when the receptors are excluded from functioning: and, 
in the third place, none of the known methods of stimulating these 
receptors would account for the salient peculiarities of the thought 
reactions. 

The outstanding characteristic of thought is that it may be 
brought about by, (1) perception, and (2) by preceding thought. 
Under the title of the association of ideas, this feature of thought 
was studied early in the history of psychology, and its laws for- 
mulated with considerable accuracy before any biological founda- 
tion was possible. Perceiving one thing makes us think of an- 
other thing : and thinking of one thing leads to— causes — the 
thinking of another. Thoughts frequently become " associated" 
or linked together in long "trains." In this respect, thought ap- 
parently differs sharply from perception, where each successive 
act needs a new stimulus. The difference is not really so great 
as it seems; nevertheless, it is important. Perceptions, other than 
those of the visceral and somatic senses, normally require stimuli 
from outside of the organism. Perceiving one thing may lead to 
the perception of another, provided the stimulus for the other is 
present. Thus, your hearing the door open may lead to, or may 
involve, the reaction of turning your head and eyes in such a 
direction that you see the person entering the room. But the per- 
ception or the thought of one thing leads to the thought of an- 
other even without the intervention of an outside stimulation. 

The requirements for the organic mechanism of the thought 
reaction are therefore clear. The mechanism must be such that a 
perceptual reaction may cause, or initiate a thought reaction, and 
a thought reaction may initiate a second thought reaction. This 
means, still more specifically, that the end of the one reaction must 
be the beginning of the other. 

Reactions end in two ways: in muscular activity, and in 
glandular activity. Glandular activity may lead to the stimula- 
tion of certain receptors eventually, but in general not im- 
mediately. The saliva secreted by the parotid and sublingual 
glands, for example, may flow into the mouth and stimulate 
touch receptors on the tongue surface. Glandular activities 
normally are rather gross affairs, the whole or a large part 
of a gland being affected in the same way. It is obvious 



300 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

that the glandular activities cannot serve as the stimuli of 
thought reactions, since the thought reactions follow preceding 
reactions immediately, and are capable of finely graded variations. 

Muscular activities, on the other hand, especially activities of 
the striped muscles, may affect receptors immediately, and are 
capable of indefinitely great complexities and variations. If we 
consider the different movements of which the arm, hand and 
fingers are capable; movements compounded from varying move- 
ment patterns of a relatively few muscles, we are impressed with 
the great range of such activities. If we consider the hundreds 
of thousands of definite and distinguishable "muscle patterns" of 
which the vocal muscles are capable in the enunciation of words, 
we are still more impressed. Since we know that all striped mus- 
cles contain multitudes of muscle spindles, in which receptors 
terminate, we know that each "muscle pattern" may give rise 
to a "stimulus pattern:" and that the distinguishability of these 
muscle patterns, so far as the individual himself is concerned, de- 
pends upon the possibility of different consequent reactions to 
the different stimulus patterns. 

We have, therefore, in the striped muscles, exactly the mechan- 
ism which the known facts of thought process demand. The 
termination of a perceptual reaction can and does stimulate re- 
ceptors which initiate a new reaction: and reactions which are 
both initiated and terminated by muscular activities may be linked 
or "associated" together almost endlessly. The conclusion that 
the muscle receptors are receptors for thought reactions is ines- 
capable. Two objections to this view are rather obvious, but 
neither is fatal. First, it may be objected that the reaction initi- 
ated by muscle action should give perception of the muscle pat- 
terns. If, in the case of visual perception, the reaction gives per- 
ception of the object responsible for the stimulation, why should 
not the same result be found in kinesthetic reaction? Why should 
not the muscular activity which is, loosely speaking, the stimula- 
tion for the following reaction, be the content perceived by that 
reaction ? 

As a matter of fact, muscle reactions do, in many cases, give 
awareness of the action which initiates them. I may move my 
arm, or speak a word, and immediately "feel" the arm move- 



THE THINKING PROCESS 301 

ment, or the vocal movements. But in many cases, even in vision 
as we have seen earlier, the immediate content, or "sign," is not 
perceived, but its "meaning" is perceived. There is no essential 
difference between these cases and the thought reaction in which 
the "sign" is a muscle pattern, and is completely unperceived 
In the case of the thought reaction, the "meaning" is called an 
"idea." 

The second objection is that there are many cases of thinking 
in which no muscular activity is apparent. Granting that in most 
cases, activities of the vocal muscles, or, in the cases of children, 
activities of limb and trunk, as well as vocal muscles, may be 
detected by methods sufficiently refined, it may be claimed that 
in some adults, at some times, the most refined methods of meas- 
urement will show no muscular activities corresponding to the 
thoughts. This objection may be solid. We may even grant the 
possibility that in many cases where the muscular activity is ob- 
servable (and these are the great majority of cases), the activi- 
ties are reduced in energy to a point where they are not capable 
of initiating the next reaction. Such a condition, at least, is to 
be expected. 

There may be, in other words, a short-circuiting mechanism, 109 
which, when the reactions have become fixed, is interposed to ob- 
viate the necessity for the second reaction in an associated series 
having to wait for its initiation upon the completion of the first. 
This short-circuiting mechanism, if it exists, functions only for 
thoroughly learned sequences: not for reactions during the proc- 
ess of learning. It would function in precisely the same way for 
series of automatic reactions, such as those involved in plain 
knitting, when this has become practically automatic. In an early 
stage of the knitting process, the completion of one set of finger 
movements is the stimulus for the beginning of the next. But this 
process is somewhat slow, and may be speeded up by having a 
shorter efferent route (shorter than the route to the arm muscles), 



i09The known functions of the cerebellum point to it as the possible short-circuiting 
mechanism. But this is so far only conjectural. Any short circuiting mechanism 
must have a "point for point " correspondence with the muscular system, so that any 
muscular pattern can be reproduced in the short-circuiting mechanism. The cerebellum 
seems to have such a correspondence with the muscular system. 



302 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

which leads to a switch-board from which the second reaction may 
be initiated before the first is completed. The muscular reaction 
still retains the possibility of checking, or modifying a wrong re- 
action. 

It is not necessary to suppose that in general, particular mus- 
cular reactions are necessarily connected with particular " mean- 
ing'' or thought-content. There is, at a given time, a definite 
muscular pattern which means a definite content, but the mean- 
ing and the muscle pattern have become connected through the 
ordinary processes of habit formation, and the connection is sub- 
ject to further modifications. This is evident at once when we 
consider word reactions. "Oiseau," "bird" and "Vogel" may 
mean the same thing, although the reactions which produce these 
sounds are very different. And many other words have exactly 
the same meaning. The meaning of any one of these words, 
furthermore, is subject to variation, without losing its general ap- 
plication. "Apple" to the horticulturist, and "apple" to the child 
who has experienced only sweet, red apples, have different mean- 
ings. So, also, other muscle patterns such as movements of the 
fingers, may have various meanings built up by habit formation, 
as in the deaf-and-dumb sign language. 

There are certain thought reactions which seem instinctive 
rather than habitual. The nodding of the head for assent, and 
the shaking for negation, are almost universal. Many "expres- 
sive" activities, like shrugging the shoulders and smiling, are not 
thought-reactions, but are emotional expressions which are 
thoroughly instinctive. It may be that all apparently instinctive 
thought-reactions are really developments of emotional expres- 
sions, as is probably the case in nodding and shaking the head. 
The question of "innate ideas" cannot, however, be settled out 
of hand. 

The reaction for the thought of an object, and the perceptual 
reaction for the same object, are essentially the same, except for 
the initiations. For a certain individual, the perception of an 
apple involves the saying of the word apple, and the thought of 
an apple involves the saying of the same word. One reaction is 
initiated by visual, tactual, or olfactory stimuli: the other is 
initiated by muscular contractions of almost any pattern which 



THE THINKING PROCESS 303 

habit lias linked up with the perception. The likeness of percep- 
tion and thought is due to their essentially identical activity: the 
•difference is in the exclusively muscular initiation of the second. 
The acquisition by a certain muscle pattern of the capacity to 
initiate a certain reaction which has developed as a perception is 
through the same sort of drainage which explains the develop- 
ment of the auditory-salivary reaction in Pavloff's dog. 110 If the 
muscular pattern is brought about in any way, at the time of a 
given perceptual reaction, the afferent current from the muscle 
pattern is drawn off into the established perceptual route, and the 
building of a habit of reaction is begun. 

Verbal language, as the great medium of thought, becomes 
more and more important relatively as civilization and the age 
of the individual advance. Most educated adults think predomi- 
nantly in vocal terms, and so the "language" of a people is the 
crystallized record of its thought processes. Most of us are, in 
fact, unable to think without actual formation of words, although 
normally we are not aware of the words, but are aware of the 
meanings. These words, in such cases, are not audible, or scarcely 
audible, since the vocal cords are not set in vibration: but aside 
from the breathing factors, the muscular patterns are quite faith- 
fully reproduced. Often, persons thinking attentively, whisper 
the words so that others can hear them. This phenomenon lies 
at the basis of some cases of alleged thought-transference, and 
some of these cases are quite free from intentional fraud, since 
it is possible for one to catch the "idea" through auditory stim- 
ulation by a whispered word without being conscious of the word 
as an auditory object at all. This is but a particular case of being 
aware of meaning without sign. 

In some cases, individuals reproduce, in thinking, not only the 
movements of the vocal organs proper, but also the breathing 
movements associated with them, and actually utter the words — 
"tnink aloud." 

Among children, and perhaps among primitive peoples, verbal 
language does not predominate so strongly. Even among some 
civilized peoples, movements of the hands, shoulders, and trunk 



nos e e Chapter XI, p. 211. 



304 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

muscles are employed in thinking, and of course in communicat- 
ing thought. Non-verbal systems may easily be acquired by any 
one. Deaf and dumb persons, although they think in "words," 
use words made of finger and hand movements, and in many cases 
these movements may be observed when the individual is merely 
' ' thinking. ' ' 

§2. The association of ideas. 

"Association of ideas" is the term which has long been em- 
ployed to denote the serial connection of thinking, and also the 
connection of thinking and perceiving which we have already de- 
scribed. "Association" is only a special case of habit formation, 
and occurs exactly as does the serial connection of reactions of 
any kind. The process can be illustrated most clearly from the 
learning of "nonsense syllables," a form of material much used 
in psychological laboratories for the investigation of association 
and memory. 

Let us suppose that a reactor is required to "learn" a list of 
six nonsense-syllables: NOF, KEV, TOL, SEB, FUD, MIP. These 
syllables are presented to him, one at a time, visually (printed 
in clear type), for one second each: and he is required to "learn 
the series," that is, to associate them serially, so that he can re- 
cite the list, beginning with the first one, without error. The 
reaction for the first syllable, in short, must initiate the reaction 
for the second, the second for the third, and so on. 

What happens is illustrated by the diagram of Fig. 31. As 
the reactor reads the syllables in succession, the reading of each 
becomes a definite reaction, which usually will be the pronuncia- 
tion of the syllables. The arcs of the several reactions are repre- 
sented in the figure by the lines NOF-N, KEV-K, TOL-T, and so 
on, representing arcs from the receptors at NOF, etc., through the 
central nervous system to the muscles, at N, etc., which participate 
in the reaction. 

The reaction NOF-N, by its muscle pattern N, excites recep- 
tors, giving rise to the afferent current n-n'. But since the next 
stimulus word, KEV, is presented before this reaction effect has 
ceased, the afferent current n-n' is "drained" or drawn off into 
the transit TOL-T, and so on. 



THE THINKING PROCESS 



305 



If the presentation and reading of the stimulus syllable is re- 
peated several times, the arcs n-k, k-t, t-s, s-f, and f-m become 
fixed, temporarily at least, and the series of actions N, K, T, S, F, 
and M may occur in the order determined by the habits formed, 
without the original stimuli. In other words, the reactor may 
"repeat the series from memory." 

In order that the series of thought reactions may be brought 
about, after it has been "learned," it is necessary to set going the 
first reaction of the series. This might be done by presenting the 



Cereb 



rum 



Cord and 
Brain-stem V 




AFFerent 
and 

EFFererit 

Paths 



Receptors I 1^ \ ]j$ $$& %W k % 

eSU- j " i k t t I s T . ' 1 



M 



Slater- 



St 



imuii 



MOP KE.V TOL 5EB FUD MIP 



Fig. 31. — Scheme of the pathways involved in the learning of a series of nonsense syllables. 
Assuming the previous development of the reactions perceptual NOF-N, KFV-K, TOL-T, SFB-S, 
FUD-F, and MIP-M, represented by the heavy lines, the lighter lines indicate the pathways 
formed from action to action, which eventually enable the successive actions to occur without 
the primary stimuli. 

first stimulus word again: but ordinarily, after the reactor has 
"learned" the series, he demonstrates the fact by reciting it with- 
out even this aid. What, then, produces the first reaction in the 
series? Or, in terminology of less definite conceptions which 
merely ascribes the successive recalls to association between 
terms, what association recalls the first term of the series? The 
explanation of the first syllable recall, although not simple, is in 
the same principle which gives the recall of the successive terms. 



306 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

In repeating the series, in learning, the last syllable becomes 
"associated" with the first, so that the completion of the series 
as presentation tends to bring abont next the reaction of the first 
syllable. Other stimuli, such as the experimenter's request to 
repeat the series: the appearance of the apparatus, at the con- 
clusion of a series, may also be associated with the first word. 
The actually important factors vary with the particular conditions 
of the experiment. In short series, however, there is a persistence 
of the first word : a preservation of the first reaction ; which it is 
at present impossible to explain. After reading a short series of 
words over but once, one can immediately repeat the first word, 
although no associations directly from the last word to the first 
have been formed. We might suppose that the recall is back- 
wards through other associations just formed in a forward direc- 
tion: but this would not explain why the first term is recalled 
before the second and third, and sometimes why the second, third, 
or other intervening terms cannot be recalled at all. 

The first reaction in such a series has especial importance, be- 
cause of the need for recalling it. The other terms may be re- 
called through the linkage of reactions, provided the first can be 
recalled. Hence the reactor in some way puts especial emphasis 
upon the first reaction, and it leaves its arc for some minutes 
ready to resume activity again when conflicting arcs are out of 
the way. The preservation of activity of elements or groups of 
elements in the nervous system must be assumed, whatever fur- 
ther hypothesis is held, in order to account for these phenomena, 
and it is not peculiar to the reaction hypothesis of thought which 
is here upheld. 

§3. Mediate associations. 

It is possible that the diagram of Figure 31 should be modi- 
fied by additional lines, showing integration of each muscle-to- 
muscle transit, with not merely the next perceptual arc, but also 
with two or more of the following arcs. That n-n', for example, 
should be shown as discharging not only into KEV-K, but also 
at TOL-T and SIB-S. Certain experimental results, to be de- 
scribed later, suggest this scheme, although it is not at present 
positively indicated. In repeating a series almost completely 



THE THINKING PROCESS 6\) ( 

learned, it frequently happens that a terra, for example, the fifth 
syllable in a list of ten, is skipped or omitted, the fourth term 
bringing up the sixth immediately; that is, the fourth reaction 
bringing about the sixth. There are many other cases, in which 
a middle term, previously associated with a preceding and with 
a following term, drops out, and the first and third terms appear 
directly associated. What actually happens in such transforma- 
tion is not known, and remains to be discovered by experimental 
work. 

§4. Formation of automatisms. 

The process in the association of ideas is precisely that in the 
habitual enchainment of actions of all kinds, whether the actions 
are ultimately conscious or unconscious. The formation of the 
habit of waltzing, i. <?., learning to waltz, may be illustrated by a 
diagram similar to that of Figure 16. The perceptual arcs, in 
this case, will be the response to the verbal commands, and pres- 
sure signals of the teacher, and the ultimate result is the forma- 
tion of a chain of reactions of the leg and trunk muscles, so that 
the movement pattern in taking the second position of the feet 
is the stimulus for the reaction of taking the third position, and 
so on: the sixth reaction being connected with the first again, 
so that the series of movements formed is cyclically connected, 
and will continue, after being well learned, with a minimum of 
perceptual control. The music, the stimulation from one 's partner, 
and from other dancers on the floor, continues, however, as a 
source of perceptual control, the dancing never being permitted 
to become a purely automatic process. 

§5. Reasoning. 

All thinking consists of reactions which may be divided into 
two classes: reactions involving neural transits already estab- 
lished by association; and reactions in which new associative con- 
nections are established. Sequences of such reactions occur un- 
der widely varying conditions, and the forms of thought are hence 
diverse. In an elementary treatise, it is not desirable to trace 
all possible forms, neither would it be possible at present to trace 
them, for psychology has only recently begun the scientific study 
of thought processes, and has, as yet, but sketched the outline of 



308 ELEMENTS OE SCIENTIFIC PSYCHOLOGY 

this study. There is, however, one form of thought into which 
it is both possible and necessary to go in some detail: this is the 
form commonly called reasoning, or inferential thinking. 

Logic deals with reasoning as an art, whereas psychology must 
deal with it from the point of view of scientific analysis. Logic 
assumes reasoning as a fact, without attempting to account for 
it, and examines the rules by which we are enabled to judge 
whether reasoning is true (or useful) or false (or disadvanta- 
geous). Psychology is concerned primarily with the explanation 
of the reaction processes which actually constitute reasoning, 
whether true or false from the logical point of view. In the study 
of reasoning, therefore, each science has its separate work, and 
neither can take the place of the other. 

The characteristic feature of reasoning is the formation of 
a judgment. A judgment, in formal logic, is expressed as a 
proposition, consisting of subject and predicate, or of subject, 
predicate and copula. "Gold is heavy," for example, is a 
proposition in which "Gold" is the subject, "heavy" the 
predicate, and "is" the copula. "Gold melts at the tempera- 
ture of 1967° F.," is a proposition in which the predicate 
is "melts at the temperature of 1967°," and the copula is im- 
plicit. Formal logic transforms this proposition into the form, 
"Gold is (a metal, or stuff) which melts at a temperature 
of 1967°," in order to make the copula explicit, because for- 
mal logic deals only with the relation of existence, which is ex- 
pressed by the copula (some form of the verb "to be") and 
does not deal with other relations and with actions. Psychology, 
however, deals with all relations, and with actions, and hence does 
not transform its judgments into the copulative logical form, al- 
though it must, of course, express them as propositions when it 
discusses them. A certain judgment in regard to a dog, for ex- 
ample, actually occurs in a form which is directly expressed in 
the proposition ' i the dog barks. ' ' Psychology examines the judg- 
ment in this form, and not in the artificial form "the dog is an 
animal which barks," which logic requires. Of course, the judg- 
ment may actually occur in the latter form in a certain case — and 
then psychology must examine it in that form ; but in either case, 



THE THINKING PROCESS 309 

the judgment must be examined in the form in which it actually 
occurs in thinking. 

A proposition always expresses a relation between a subject 
and a predicate, or between a subject and objects not specified, 
as in the instances given. For an act ascribed to a subject always 
involves relations between the subject and other objects. From 
the nature of the proposition we may arrive at the nature of the 
judgment, since it should make no essential difference whether 
the judgment occurs as a reaction or reactions involving the vocal 
muscles, or some other muscles. In any case, the judgment is 
a succession of two thought reactions: and the content of at least 
one of these is a concept, involving a relation or relation-complex 
to the content of the other, or else involving the other with a 
relation or relation-complex added. In thinking t ' the dog barks, ' ' 
in any way, there is a reaction involving awareness of "dog," and 
a second reaction, which may be a particular idea, involving the 
same "dog" with the added relational system of "barking activ- 
ity." In the judgment "Gold is heavy," the first idea may be 
a concept including the relation (to the earth and other objects) 
"heavy," and the second may then single out for its content the 
relation "heavy" already included in the first content. This judg- 
ment is commonly called analytic, and the first one is called 
synthetic. In the synthetic judgment, the second idea is richer 
in content, in some respect, than is the first: in the analytic judg- 
ment, the second idea has for its content a limited part of the con- 
tent of the first, or at least a limited part of the content is more 
vividly attended to than in the first. Judgments must, in gen- 
eral, fall under one or the other of these classes, unless the sec- 
ond idea is merely the repetition of the first, in which case we 
do not speak of the sequence as a judgment, but call it the repeti- 
tion of an idea. 

The succession of thought reactions in a judgment may be 
merely one which has become habitual. In that case, the series 
follows the general law of habit, and requires no special consider- 
ation in this place. The important matter is the formation of a 
new judgment, that is, the formation of a new sequence of thought 
reactions of the sort we have been describing. 

The formation of an analytic judgment depends upon condi- 



310 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

tions which are usually A T ery complex, involving the residual ef- 
fects of many preceding stimulations and reactions. There is no 
simple and general set of conditions which can be described as 
accounting for the process. The difficulties in respect to an 
analytic judgment are precisely similar to those in respect to 
analytic perceptions. Often, the perception of an object as a whole 
is followed by the perception of a limited part of the same ob- 
ject, as in the case where you perceive some one's face as "odd 
looking," and then perceive one eye as having a cast in it. Such 
instances of analysis are so common that we may never reflect on 
the difficulty of explaining them. The analytic judgment is of 
precisely the same type, and together with the analytic percep- 
tion constitute an important problem for psychological study, a 
problem which so far has not been attacked seriously, and con- 
cerning which it is of little use to theorize. 

The conditions determining the synthetic judgment are simpler, 
involving the established principles of habit formation in an in- 
telligible way, although the process is modified and directed by 
the same complex effects of preceding reactions which determine 
the formation of the analytic judgment. Here, also, the condi- 
tions are closely paralleled by those determining a certain form 
of perceptual development, and we may usefully consider the per- 
ceptual and the ideational processes together. 

Suppose that in a salesroom you are examining an electric 
toaster placed before you by the salesman. You perceive it first 
as "electric toaster," the reaction involving that perception hav- 
ing been built up by a succession of preceding reactions. But 
you do not perceive it as "good toaster." Next, you perceive the 
label "Genax Electrical Company," whereupon the toaster is per- 
ceived as "made by Genax," and immediately thereafter the 
toaster is perceived as "good toaster" (toaster it is safe to buy). 
This process, as described occurs if you have previously formed 
the concept of "Genax products" ("manufactured by Genax"), as 
"good" products, so that the action-pattern "Genax product" 
initiates at once the reaction terminating in the action-pattern 
' ' good, " or " good Genax product ' ' ( synthetic form) . If this con- 
ceptual and judgmental tendency has been established, the con- 
stant drainage tendency of the central neurons establishes the 



THE THINKING PROCESS 311 

connection between the stimulus pattern of the particular toaster 
and the action pattern of "good," and the toaster is perceived as 
good. 

A closely similar process occurs where the object (correspond- 
ing to the toaster) is not perceived, but thought-of, and the modifi- 
cation of the original reaction, involving an addition to or modi- 
fication of the original content, is brought about in any way what- 
soever. Assume that the transaction is not completed in the sales- 
room, because the completion of the synthetic judgment is in- 
hibited by failure to notice the label, or by the absence of the 
judgment "Genax products are good." Later, perhaps by tele- 
phone, the information as to the label is received; or the judg- 
ment characterizing this firm's products is formed through con- 
sultation of some one whose judgments on such points you adopt ; 
and the synthetic judgment may be completed. 

The foregoing brief sketch of certain features of reasoning is 
useful merely as an indication that it is possible to work out the 
psychological details of complicated thought processes in a scien- 
tific way, and that the work still remains to be done. Although 
logic has treated reasoning from its point of view in a compre- 
hensive way, psychology has so far done very little in this part 
of its field. Psychologists have, in the main, pursued two policies 
here: either they have left reasoning processes out of considera- 
tion, or they have treated them purely from the logical point of 
view, the paragraphs on this topic in many text books being but 
paraphrases of the logician's treatment. This has not been for 
want of interest or want of appreciation of the importance of the 
topic, but from the lack hitherto of a scientific basis from which 
psychological development is possible. We may confidently ex- 
pect that there will be, in the immediate future, experimental 
work in this field, and the reproach that experimental psychology 
concerns itself almost exclusively with sense perception will be 
removed. 



CHAPTER XV 
AFFECTIVE EXPERIENCE 

§1. Feeling and emotion. 

In the. preceding chapters, we have apparently neglected a 
large and important class of content, and the reaction processes 
through, which it is perceived. Sentienda and relations make up 
the outer world: but there is an inner world of feeling which is 
just as real as the outer world, and in some respects more impor- 
tant. What is this inner world, and how do we experience it? 
The answering of this question can be delayed no longer. 

Under the general names of "feelings and emotions " we cus- 
tomarily include such things as joy, rage, melancholy, pain, 
hunger, fatigue, thirst, amourousness, irritation, pleasure, desire, 
and sometimes even such obviously sensory contents as tickle, 
warmth and touch. The apparent nondescriptness of this group 
of things has led to a distinction being raised between the obvious 
sentienda included in the group, and those things which are less 
obviously sentienda, and the application of the terms affections, 
affects or affective contents to the latter. Whether this distinc- 
tion is useful or harmful will be considered later. 

Among the affective contents, it has been the custom of psy- 
chologists to distinguish the simpler affects from the more com- 
plex, and to apply the term feelings to the former, and the 
term emotions to the latter. In popular usage, however, although 
the term "emotion" has been restricted as among psychologists, 
the term "feeling" has been applied to the whole group. There 
seems to be no use in attempting to oppose popular usage on this 
point, and we shall therefore follow it. 

§2. The nature of feeling. 

Feelings are actual data in experience. They are facts, not 
inferences; and they are content of which we are aware. They 
are comparable to sentienda, in that they have intensity, duration, 
and sometimes even extensity, and are spatial to the extent of 

312 



AFFECTIVE EXPERIENCE 313 

being located within the body. Not only the feelings which are 
classed as sentienda, such as pain and fatigue: but also the un- 
questionably affective contents such as joy, amorousness, and 
rage, are distinctly within the confines of my body; not in the 
outer world, and not, like awareness, exempt from space limita- 
tions. 

Feelings, then, must be something experienced through reac- 
tions which are initiated by the stimulation of receptors just as 
sentienda are experienced. We might say that feelings are per- 
ceived, but it is better to retain the term perception to apply to 
external perception only, and apply the more general term in- 
tuition to internal experiencing. 

The existence of a class of sentienda (pain, warmth, fatigue) 
which are persistently classed with feelings, and the existence of 
a second class of content, (hunger, thirst, fullness, etc.) which 
are sometimes classed as sentienda and sometimes as affects, gives 
the clue to the real nature of feelings. They are organic, or bodily 
sentienda : details of the soma and viscera, and of changes in soma 
and viscera, as those details and changes are intuited or experi- 
enced. The classification of warmth, cold, pain and pressure as 
feelings is quite intelligible. In so far as warmth and cold are 
properties of the body, they may truly be feelings. In so far as 
they are properties of external objects, they cannot be feelings. 

But even those contents which are always properties of the 
body may at times not be feelings. Pain, always in the body, 
may be a feeling, or it may be a sentiendum of the organic sense. 
Hunger and thirst are not classed merely inconsistently now as 
feelings, now as sense data. Actually, these data may be feel- 
ings at one time, and not at others. 

The essential characteristic of a feeling is its vagueness and 
lack of definitely perceived pattern. It is not even definitely 
localized; in its most truly characteristic condition, it is just " in- 
side. " However complex it may really be, its complexities are 
not perceived. In so far as the feeling is analyzed and localized, 
it ceases to be a feeling and becomes organic sense-data. The 
emotion as intuited may be compared to the sound of an orchestra 
to a man who has previously heard no musical instruments, but 
whose auditory mechanism is perfect. The sound is to him a vast, 



314 ELEMENTS OE SCIENTIFIC PSYCHOLOGY 

insistent, general noise, however rich and impressive it may be. 
The shrilling of the chorus of strings in one passage, and the blar- 
ing of the brasses in another may be markedly different to him; 
but he discriminates no details in either. The sound to him is 
actually a feeling, 111 added to his complement of bodily feelings. 
Even to the partially sophisticated listener, and to the trained 
listener, in his unanalytical moments, the orchestral synthesis has 
a feeling characteristic, which is lost when the pattern is analyzed. 

The bodily sentienda are preeminently fitted to merge as feel- 
ings, because of the great difficulty in analyzing and localizing 
them. The auditory, dermal and visual data are analyzable be- 
cause they are readily variable. By controlling the stimulus, and 
by motor adjustments, fine variations are produced in the stimula- 
tion, and the data are thereby analyzed. But in the case of the 
viscera, and to a large extent, in the case of the soma, gross varia- 
tion in stimulation, and that not readily controllable, is the most 
that is possible. 

The organic sense data, therefore, remain largely feelings; the 
rich and general background of experience against which external 
objects are perceived, and are analytically reduced to mere sense 
data only by great labor, and even then only in small part. For 
this reason it is inadvisable to speak of "perceiving" the emo- 
tion or feeling, but rather to speak of apprehending or "intuit- 
ing" it, since "perception" usually connotes an analytical aware- 
ness in which details of the content are to some extent dis- 
tinguished. 

§3. Feeling and reaction. 

The possibility of experiencing feelings depends primarily upon 
the receptors which have their distal terminations distributed 
through the soma and viscera. These receptors have their cell 
bodies either in spinal ganglia, or in cranial ganglia, and send 
their dendrites to the viscera through the autonomic division of 
the nervous system: and to the striped muscles, tendons, fascia, 
and skin, through the spinal and cranial nerves. 

The visceral organs are the most important source of feeling, 



niThis is, of course, over and above the bodily feelings aroused by the music, al- 
though the latter are directly affected by the former. 



AFFECTIVE EXPERIENCE 315 

and hence the afferent autonomic system is the most important 
''sensory" system for feeling: but we must not forget that mus- 
cular and even dermal components enter into many emotions. The 
muscular system plays a complicated role in mental life. 

If we consider in detail the various tissues and organs of the 
body in which receptors terminate, we obtain some conception of 
the possible range of bodily qualities. The skin and mucous mem- 
brane we have considered already. There are sensory endings 
in the superficial fascia which lie between the skin and the striped 
muscles, and in the deep or inverting fascia, which lie between 
the muscular layers in certain parts of the body. The omenta 
and mesenteries which suspend and bind the stomach and intes- 
tines; the peritoneum and pleurae, which line the abdominal, sacral 
and thoracic cavities, and in part cover the viscera externally; 
the periosteum, which covers the bones; and the perimysium, 
which envelopes and penetrates striped muscles, are also connec- 
tive tissue structures which are supplied with sensory neurons. 

The heart, and the bloodvessels throughout the soma and 
viscera, have sensory endings either in their connective tissues, 
or in their muscles. The various parts of the alimentary canal — 
gullet, stomach, small and large intestines — contain receptorial 
terminations, at least in their connective tissue coats and epithe- 
lial linings. The urinary system of kidneys, bladder and ducts, 
and also the liver, pancreas and the other glands, are all supplied 
with afferent fibers. The generative organs, not merely the ex- 
these receptorial systems may be points of origin of reactions, and 
internal organs of both, have a rich afferent supply. And all of 
these receptorial systems may be points of origin of reactions, and 
hence of affective experience. It is worth while even to inquire 
whether there may not be receptors in the nerve tissue itself, since 
the feeling of interest seems to be an actual state of the nervous 
system, and not of any of the non-neural tissues. How many di- 
verse feelings can arise in each of these tissues and organs, and 
to what extent the same feeling may arise in different structures, 
remains yet to be discovered. 

§4. The simple feelings. 

There are a number of feelings which appear to be simple, and 
which may be considered as at least relatively simple: (1) sus- 



316 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

pense, (2) disagreeableness, (3) pleasantness, (4) excitement, (5) 
fatigue, (6) strain, (7) relaxation, (8) depression, (9) thirst, (10) 
fullness (of alimentary canal and bladder), (11) emptiness, (12) 
malaise, (13) nausea, (14) dizziness, (15) exhilaration, (16) in- 
terest, (17) a localized sex-feeling, (18) suffocation, (19) relief, 
(20) satisfaction, (21) revulsion, (22) tender feeling, (23) antici- 
pation, (24) choking, (25) retrospection, (26) desire, and, of 
course, pressure, pain, warmth and cold. Undoubtedly there is 
an enormous number of other feelings which are as nearly simple 
as these, but which have not as yet been analyzed out of the com- 
plexes in which they occur. 

A number of the feelings listed above are, perhaps, not simple, 
but complexes of simple feelings, and may eventually be analyzed 
into their elements. They function, however, as rather constant 
radicals, if they are not actually simple. Some of them may seem 
to be types including a number of qualitatively different feelings, 
rather than single feelings. 

There is a recognized difference, for example, between fullness 
of the stomach of the small intestines, of the colon, of the rectum 
and of the bladder. There may seem to be different sorts of ex- 
citement and relief, irritation and satisfaction. But it is quite 
probable that the differences are not in the feelings named, but 
in attendant feelings of other sorts, which uniformly accompany 
these feelings. The attendant feelings in some cases of fullness 
seem to be peculiar to the organs in which the fullness arises; 
but in other cases, they probably arise from different organs or 
tissues, or from definite processes therein. 

The great mass of feelings such as hunger, pleasure, joy, sor- 
row, fear and the whole list of emotions, seem to be complexes 
of the feelings named above, together with feelings as yet un- 
named, and the great variation in these emotions and other com- 
plex feelings undoubtedly depends upon the variation in the ele- 
ments or radicals present. These variations are so great that 
there is no possibility of a sharply defined classification of the 
emotions. Consider, for example, the closely related and relatively 
simple emotions of approval, disapproval and pathos. Approval 
includes satisfaction (apparently an alimentary feeling localized 



AFFECTIVE EXPERIENCE 317 

in the gullet and stomach) with some pleasantness, a slight ele- 
ment of relaxation, and several feelings not yet analyzed. Dis- 
approval includes revulsion (also an alimentary feeling) as its 
most prominent element, together with disagreeableness, some 
strain, and other feelings. Pathos is not a combination of ap- 
proval and disapproval, but combines the satisfaction and revul- 
sion, which are the most characteristic components or' these two, 
with an element of excitement, and varying other components 
from approval and disapproval. Sometimes there is strain, some- 
times relaxation: sometimes pleasantness, sometimes unpleasant- 
ness. 

Certain of the feelings are characteristically arranged in op- 
posing pairs. Strain and relaxation, pleasantness and unpleasant- 
ness, satisfaction and revulsion, fatigue and exhilaration, fullness 
and emptiness, malaise and relief, are such pairs. This antago- 
nistic relation suggests the dependence of the pair on the same 
organ or tissue, under opposed conditions. Strain and relaxation 
are probably muscular. Emptiness and fullness are of course de- 
rived from opposing conditions of the bladder and alimentary 
canal. Satisfaction and revulsion may be associated with the 
peristaltic and antiperistaltic movements of the gullet and stom- 
ach. This does not mean that both members of a pair may not 
actually be present in a single affective content, since one part 
of an organ or system of tissues may exhibit one action or con- 
dition, while another part exhibits the reverse. Pleasantness and 
unpleasantness, however, seem to be conditions or processes in 
some organ or system which cannot work partially, but goes as 
a whole. The most plausible processes as a basis for these feel- 
ings have been claimed to be the tumescence and detumescence of 
the erectile parts of the generative organs, but this assumption 
is merely tentative, and hardly yet sufficiently indicated as a 
working hypothesis. We should remember, however, that these 
processes are demonstrable in the very young baby, in whom they 
have not as yet become a true sex function, and that their feeling 
significance is unquestionably much wider than the sexual or re- 
productive emotions. 



318 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

§5. Emotions, moods and sentiments. 

An emotion is a process which lias a definite conrse of rise, 
duration and subsidence, and is usually dependent upon (really 
caused by) an external stimulus pattern. In the case of anger, for 
example, a stimulus pattern which may consist of a blow, word 
or visual details, causes a reaction which terminates in profound 
visceral disturbances, together with somatic changes. The reac- 
tion involves the perception of the affront, or threat; and its 
organic termination pattern (involving activities of smooth and 
striped muscle, glandular activities and probably other chemical 
changes) really is the emotion of anger. This action pattern is 
also a stimulus pattern, since it stimulates receptors terminating 
in the visceral and somatic tissues, and thus initiates a new reac- 
tion, in which the emotion is experienced. If the afferent fibers 
from the soma and viscera were blocked, but the efferent fibers 
to these tissues not interfered with, the emotion would occur, but 
it would not be experienced. The animal would exhibit all the 
expressions of anger but would not experience it. 

In such emotions, two groups of component content may be 
distinguished. (1) A quick component, due to the activity of the 
muscular systems, both the striped and the smooth. Tension of 
muscles of the back and limbs; violent contraction of certain 
muscle groups, as in "starting," alteration of the breathing proc- 
ess and heart beat, alteration in arterial tension, evidenced ex- 
ternally by flushing and paling, contraction and relaxation of the 
urinary and anal sphincters ; and important changes in peristaltic 
and other activities of the alimentary canal; are familiar facts in 
emotion, and these occur as the immediate termini of the percep- 
tual reaction and as the immediate initiation of new reactions. 
(2) The glandular effects, however, do not affect receptors so 
quickly. Increased and decreased secretion of the adrenal, thyroid 
and other glands require some seconds to affect the visceral and 
somatic stimulus pattern, since the secretions (hormones) of the 
ductless glands must be carried in the blood stream to other parts 
of the organism. These gland products are effective by chang- 
ing the activity of muscle, and probably also as direct chemical 
excitants of receptors terminating in various connective tissues. 

The quick and slow components may be recognized readily in 



AFFECTIVE EXPERIENCE 319 

such an emotion as fear, due to a sudden stimulus. In some cases, 
the quick component occurs, with the slow component so minimal 
that we call the complex not fear, but "being startled." The 
comparison of these two emotions gives some notion of the im- 
portance of the visceral activities, as compared with the somatic, 
and also of the difficulty in estimating the nature of an emotion 
by its externally perceptible factors. An emotion of fear in which 
the activity of the striped muscles is very small may be ex- 
tremely intense because of powerful visceral reactions, and an 
emotion in which there is a strong external factor of the sort com- 
monly present in fear may have little of the fear characteristics 
because of the mildness of the visceral factors. The comparison 
of the emotions of children with those of adults is especially dif- 
ficult on this account. We are unable at present to determine 
whether children under two years of age really experience any 
emotion such as adults call "fear." 

In addition to definite emotions, there are organic conditions 
of relatively prolonged duration, which are conventionally called 
moods. A mood may be described as being in part a tendency 
to be thrown easily into an emotion, or simpler feeling, of a defi- 
nite type. A reactor in an angry mood is easily roused to anger 
by external stimulus patterns which, in other moods, would 
not anger him. In a depressed mood, occurrences which would, 
ordinarily be innocuous, bring on a strong feeling of depression. 
In an elated mood, trivial situations call forth joy or other elated 
emotions. These moods are familiar facts in the lower animals 
as well as in men, and may be due to maladjustments or perfec- 
tions of functioning of the organism, quite aside from specific ex- 
ternal stimuli, or they may be due largely to the effects of environ- 
mental factors on the organism. Nervous disease, glandular dis- 
ease, febrile conditions, digestive disorders, drugs such as alcohol 
and hashish, loss of sleep, variation in sexual function (such as 
the menstrual cycle in the female), over-work, general well-being, 
worries, failures in important projects, success and flattery, over- 
stimulation of visual and auditory functions, and a host of other 
external and internal conditions, have their well marked conconm 
tant moods. The "lioness robbed of her whelps," and the "strong 
man rejoicing to run a race" are classic illustrations of moodi- 



320 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

ness. For the unusual affective response of our friends we daily 
seek explanations in conjectured occurrences or ailments which 
could be responsible for the moods they display. 

Moods are in most cases more than mere " tendencies" which 
might be ascribed to the nervous system alone. Some trace, often 
a considerable one. of the feeling or feeling complex persists as 
a continuous content during the time the mood lasts. In an irri- 
table mood, the irritated feeling may be continuous, rising to in- 
tense pitches when certain stimuli operate, and sinking to a lower 
level during the interval between such stimuli. The angry mood 
is more than a succession of fits of anger, with the "tendency" 
bridging the gaps: It involves in many cases a persistence 
of the angry feeling, even when there is no anger at or over spe- 
cific stimulus-patterns. Depressed and elated moods especially, 
showing a continuous depressed or elated feeling, are not de- 
pendent upon any specific external occurrence. These persistent 
feelings are especially marked in the insane and neurotic, in many 
of whom no combination of external impressions can inhibit the 
depression or elation, even temporarily, while the mood lasts. 

In this continuousness is the chief distinction between a mood 
and an emotion. The emotion, aroused by a specific stimulus- 
pattern, is integrated consciously with the object or event 
concomitant with that pattern. The emotion is experienced as a 
background for, or adjunct to, the object or event perceived, the 
perception of which is the real cause of the anger. When a man 
steps into the seat I have vacated for a moment, my anger is at 
his act. That is: I experience the anger and his act as a single 
pattern. And in such a case, the emotion subsides with the sub- 
sidence of the perception or thought which aroused it. I do not 
carry the emotion over to other objects and other events, which 
would not in themselves arouse it. 112 

The characteristic of the mood is that it attaches to, and is 
experienced with, a wide range of objects and events which stim- 
ulate the reactor while the mood persists. If I am really in an 
angry mood, I not only am intensely angry at the act of the man 

i!2lt is true, however, that a strong emotion may leave a transitory mood of the 
same kind behind it. Often, however, it has the reverse effect, and leaves the reactor 
less susceptible to stimuli which normally arouse that emotion. 



AFFECTIVE EXPERIENCE 321 

wlio usurps the seat: I am angry with the innocent passenger who 
is thrown against me by a lurch in the car; I am angry with the 
conductor who seems to be slow in giving me my change; I am 
angry at the newspaper which refuses to fold conveniently for 
my reading; and at a long list of petty circumstances which are 
effective really because the anger is there, ready to be attached 
to any object, and to rise in intensity in the process of integra- 
tion. 

In contrast with these tendencies to specific emotional reac- 
tions without much distinction of stimuli, there are tendencies to 
systems of specific emotional reactions, each under specific en- 
vironmental conditions, but dependent upon definite functional 
conditions of the organism, which are of great importance. These 
systematic tendencies are called sentiments. 

Patriotism and parental love are conspicuous examples of senti- 
ments. The parent who loves the child is in such an organic con- 
dition that he experiences tender emotions when he caresses, or 
even when he contemplates the child, in the absence of conflict- 
ing stimulations. If the child is injured, he experiences grief; 
when he perceives or thinks about the child's condition as such. 
When he is aware of the act of some one which injures or threatens 
the child, anger arises. When the child shows desirable traits, 
pride enters. If the child is vicious, chagrin or shame occurs. 
And so on, through practically the whole range of emotions and 
simpler feelings. No one of these emotions, nor the whole gamut 
taken together, constitute parental love: parental love is the ten- 
dency, resident in the organism, and organized by the circum- 
stances which have made the man a parent, to experience these 
emotions in a definite and predictable way, as results of specific 
environmental patterns into which the child enters. 

§6. The driving force of feelings. 

While considering the feelings as products, we must not ignore 
their functions as causes. The effects of feelings in the reactions 
which follow them are profound, and the method of production 
of these effects is made clear by the analysis which scientific 
psychology makes of the feelings themselves. A feeling is always 
a real organic process or condition, and is a stimulus pattern 



322 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

which is the beginning of a reaction pattern. The feelings are 
powerful stimuli, and the effect of the reactions they initiate are 
among the most important determining influences in our total 
reaction system; not more important than the hereditary consti- 
tution of the reactive machinery, but important as the chief means 
through which both hereditary tendencies and the modifying ef- 
fects of the environment operate. 

The afferent current derived from feelings must release effer- 
ent current which must go somewhere, to some muscles and 
glands, and must produce important effects. If the succeeding 
perceptual and thought reactions draw off this efferent current 
into their proper channels, the results of these reactions may be 
usefully intensified and extended. In this case the emotions are 
said to be "under control." The emotional discharge, however, 
may seriously interfere with the normal efferent discharge pat- 
tern of the perceptual and ideational reactions, either making 
these latter ill adapted for the proper adjustment to environment, 
or even blocking the normal efferent pathways completely by 
drawing off the discharge into new wholly emotional responses. 
In such cases the emotions are said to be "uncontrolled." To 
say that control of emotions is the most important thing in life 
is trite, but the saying can hardly be overemphasized. 

It has long been surmised that feeling is the most important 
controlling factor in the learning process, and its function here 
has been questioned only because of a confused view of psy- 
chology in which the feelings were considered as a sort of "purely 
mental" content, quite remote from the world of muscles, glands 
and actions, and therefore having no means of influencing that 
world. Of course, feelings are as "mental" as any object or con- 
tent can be: but they are also real, effective factors in the body, 
as "common sense" has long supposed, and as scientific psy- 
chology explains them to be. 

The confused view which psychology formerly had regarding 
the feeling is partly responsible for our lack of detailed informa- 
tion concerning the practical working of feelings in connection 
with perceptual and thought reactions. The extreme difficulty in 
experimental work on feelings is the other cause of our ignorance. 
The study of feeling is one of the most important tasks of experi- 



AFFECTIVE EXPERIENCE 323 

mental psychology in the future, and there is no ground for doubt 
that the study will advance satisfactorily. Too much effort has 
been put in the past into the so-called "introspective method" in 
studying feeling, and the substitution of the experimental method 
will unquestionably make future efforts more profitable. 

Certain practical points in regard to feeling and the learning 
process are fairly well established. Pleasant emotions, if of mod- 
erate intensity, are favorable to the fixation of habits, and un- 
pleasant emotions inhibit the fixation. Both, therefore, may con- 
tribute to the learning process. Reward and punishment as aids 
to learning are both practically and experimentally approved. 
Strong emotion of any kind is apt to be detrimental: the general 
consideration of the connection of feelings with reactions would 
lead us to expect this Interest in the stimulus pattern is pro- 
foundly effective in all kinds of learning, and desire of the fin- 
ished result is also of great importance. With regard to other 
details, we have nearly all to learn. 

§7. Desire or conation. 

Desires are feelings of especial importance, apparently vital 
in their bearing on life. Without desire the complex animal would 
probably not adjust himself to the environment, and would shortly 
die as a result of mal-adjustment. 

It might be supposed that there is only one sort of desire, and 
that the difference between the various "desires" is a difference 
solely in the perceptual or thought content to which the desire 
attaches. While it is true that in many cases the desires are dif- 
ferentiated solely by their objects, it seems probable to the author 
that there are several fundamentally different desires and that 
these desires are resident in specific parts of the organism. It 
is not to be assumed at present that these desires are literally 
simple. They may be complexes; but if so, they are of a rela- 
tively constant sort, (quasi-elements or radicals) the constituent 
elements in any one sort of desire being united in a rather in- 
variable way, and functioning as a group or radical. If that be 
true, it may also be true that in all desires there is one common 
element. Nevertheless, the several sorts of desire would still be 
differentiated bv their characteristic non-common element. 



324 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

The list of desires which is proposed as fundamental is as fol- 
lows : 

1. Desire of aliment (food and drink). 

2. Desire of excretion (to be rid of disturbing things). 

3. Desire of rest. 

4. Desire of activity. 

5. Desire of shelter (protection from disagreeable factors in 
the environment). 

6. Desire of conformity (doing as others do, or as a leader 
does). 

7. Desire of preeminence (leadership). 

8. Desire of progeny (parental desire). 

9. Desire of sex gratification (amatory desire). 

These desires are designated by their most common objects, 
but this is merely a matter of description; ultimately we must 
identify them in some more direct way. 113 All of these may attach 
to objects of certain other types, and by such attachments, and 
combination of attachments, all the specific desires arise. Some of 
these primitive desires can perhaps attach to the objects to which 
the other desires also attach; but this is not possible throughout, 
and such attachment is perhaps rather exceptional than typical. 
Amatory desire and parental desire, for example, when attached 
to the same person, form a distinctly pathological combination, 114 



nsWe might speculatively assign the desires to the various parts of the body as 
follows: 

1 & 2. Alimentary canal and urinary system: associated with hunger, thirst, full- 
ness, emptiness, etc. 

3 & 4. Striped muscles: strain, relaxation, fatigue, etc. 

5. Skin, mucous membrane and connective tissue: feeling of cold, warmth, pres- 
sure, pain, etc. 

6 & 7. Circulatory and respiratory systems. 
8 & 9. Sexual organs. 

Such assignment is, however, to be regarded as merely illustrative of the definite- 
ness of organic connection which is to be sought; not as prophetic of the results of 
final analysis. There- is some reason to believe that activity of skeletal muscle is 
important in all desire. 

114 Such a combination exists in certain cases in which a father has an amatory desire 
toward his own daughter, or a mother toward her son. Also in cases in which a wife 
"babies" her husband, or a husband assumes a parental attitude toward his wife. 



AFFECTIVE EXPERIENCE 325 

and when these two desires are normally combined, in the 
same total content, their objects are discriminably different. 

Desires have both positive and negative aspects, in this re- 
spect suggesting the paired feelings. In place of desire of an 
object, there may be aversion, or repugnance to it. "While it is 
possible that aversion for given objects may ultimately be ac- 
counted for as a combination of desires inhibiting the otherwise 
possible desire for that object, such explanation does not at pres- 
ent seem possible, and we must consider aversion along with de- 
sires. We shall speak principally of the desires in the following 
pages, but must be understood always to be including the con- 
trary conations. Since there is no accepted verb corresponding 
to aversion, we shall use the term repugnance, with the verb 
repugn, whenever we speak directly of these negative desires. 

The practical impoitance of the desires is beyond question. 
Mere fatigue, for example, is not sufficient to impel the animal 
to take sufficient rest. Any one who has had the care of children 
knows that this is true. The sight of a child fighting against 
fatigue and the sleep tendency, and refusing to go to bed is 
familiar. And the tendency of children to go on with exhaust- 
ing play in spite of extreme fatigue is also well known. The ex- 
citing stimulations in such cases do not inhibit the fatigue, but 
do inhibit the desire to rest. Even in the case of adults, the 
exigences of economic effort, and stimulation of complicated soc- 
ial life frequently lead to man's denying himself needed rest. 
Neither does the buffeting of the weather, or any other action of 
the environment, always suffice to draw an animal to shelter, or to 
ward off the injurious influences. For purposes of illustration, 
we may point to the cases in which the human animals expose 
themselves to inclement weather in response to the dictates of 
fashion, or sit in the cold rain to watch a football game. Hunger, 
or sex desire, or fear, may inhibit the shelter desire in the lower 
animals, and cause them to expose themselves to conditions from 
which the shelter desire normally protects them. Even bears, in- 



The passion for pot dogs displayed by some women is of a doubly perverted type: 
being not only the transference to a lower animal of emotional intent which should 
be expended upon human objects, but also the combination of the parental and amatory 
tendencies upon the same object. 



326 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

sufficiently provided with fat against the hibernating period, have 
been known to break its customary inhibitions. 

In the case of activity, full capacity and full need may be pres- 
ent in an indolent person, without the effective desire. In the 
lower animals, natural selection perhaps eliminates the indolent; 
but in modern civilization, the indolent man, unfortunately, is 
often nourished and allowed to propagate his kind. The desire 
of activity produces its most striking manifestation, quite apart 
from the impelling force of food, progenic and amatory desire, 
in the piay activities of the young. In play of both man and 
beast, even the desires of conformity and preeminence are fre- 
quently absent, although these easily and characteristically 3nter 
into the play activities of groups, both human and infra-human. 

Where parental desire is absent, amatory desire produces 
activities of a type which are decidedly lower than those in which 
the two sex desires combine. Such activities are lower in evalua- 
tion both from the point of view of general and of social psy- 
chology, and are powerful illustrations of the importance of de- 
sires. Parental desire without amatory, on the other hand, also 
occurs and likewise produces disastrous results. Marriage in 
which there is no amorous attraction between husband and wife, 
although relatively infrequent, is unfortunate, even for the pur- 
pose of satisfying the parental desire, and no child should be 
subjected to the influence of a home so constituted. 

In their relation to the reactivities of the organism, desires 
follow the general laws of integration and habit formation to the 
full. Desires may be attached to new objects, and detached from 
primary objects, by the operation of drainage and repetition in 
the usual way. Objects which are associated with desired ob- 
jects come to be desired, and objects associated with repugned 
objects come to be repugned. In this connecting or associating 
process there is, however, a distinct selective tendency: those ob- 
jects (or events) which are causes of desired (or repugned) objects 
come to be desired (or repugned), but those objects which are 
effects of desired (or repugned) objects do not so uniformly come 
to be desired (or repugned). Desire " spreads" generally in the 
line of ascending causation: less generally in the line of descend- 
ing causation. This point is of great importance, not only for 



AFFECTIVE EXPERIENCE 327 

the understanding of the process of substitution of desires, but 
also for the understanding of the role that desire plays in the 
general iearning process. 

Desire ceases with the attainment of the object. In more 
scientific terms: desire attaches to (is integrated with) an antici- 
pated thought object; never with a presently perceived object, or 
a retrospective thought object. Whatever feeling may be inte- 
grated with an object once desired, but now perceived, desire is 
absent. The same object, retrospectively thought of, is not de- 
sired, unless there is also an idea of it as again possible: that is, 
an anticijjatory idea. The perceived object can be desired only 
indirectly, that is, only in so far as there is an idea of its con- 
tinuing to be perceived. The anticipatory idea is a prime essen- 
tial. While we cannot at present assign the organic basis for 
this peculiarity of desire, it is an indisputable fact. 

Now the general conditions for the formation of an associa- 
tion are that the two things to be associated or integrated must 
be perceived or thought of in close temporal succession, or 
simultaneously. Tt is obvious, therefore, that in thinking of the 
cause of a desired event (the cause of obtaining a desired object), 
the desire is in many cases experienced in close temporal sequence 
or precedence: and that in thinking of a desired event, one fre- 
quently is impelled, by already established associations, to think 
of the causes. But in desiring an event, one is less apt to think 
of its effects, and when the effects occur, and must be experienced, 
the object is no longer desired but is retrospectively thought of. 
The conditions are therefore generally excellent for associating 
a desire with the cause of the desired event; generally not good 
for the association of the desire with the effects. The general 
spreading of desire in the line of ascending causation is, there- 
fore, what the laws of habit formation would lead us to expect. 

It is probable that the chief, although of course not the only, 
process through which desires are substituted is through the al- 
ready formed association of cause and effect. But after a desire 
has been attached to an object or event through this process, the 
laws of habit still hold, and the new object or event may con- 
tinue to be desired, independently of the original or primitive 
desire for the original object or event. A man who acquires a 






328 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

desire for work through the association of work with food, shelter, 
sex gratification, or preeminence, which are primarily desired, 
may often acquire a permanent desire for work which persists 
after the primary desire has ceased. So a person who engages 
in social activities, or in meticulous attention to details of dress 
as a step towards the furtherance of a social ambition, comes to 
desire these things in themselves. 

Primitive man, in a healthy state, shows all the nine desires 
listed; but if natural conditions are such that the alimentary and 
shelter desires are easily satisfied, further development of desires 
by substitution is relatively small, and culture remains in a simple 
stage. If food and shelter are easily obtained, the satisfaction of 
the parental and amatory desires are complicated only by the 
rivalry for mates, which introduces desire for ornament, warfare, 
and social activities (such as dancing) of a simple kind. Unless 
population increases rapidly, society soon reaches a stable state, 
in which desires are standardized on a permanent basis. The de- 
sires for preeminence and conformity are satisfied on the basis 
of warfare and the other simple activities described. In a trop- 
ical climate, with abundant food, and few natural enemies in the 
way of disease and deadly animals, culture apparently would re- 
main indefinitely in this stage, as in the South Sea Islands before 
the advent of the white man. 

In colder climates, where both shelter and food are obtained 
with difficulty, not only are the satisfactions of these desires made 
more intricate, through the introduction of many new desires for 
objects and processes causally connected with the satisfaction of 
alimentary desires, but also, on account of the difficulty in pro- 
viding for wives and children, the satisfaction of amatory and 
parental desires is made immeasurably more difficult, and vast 
numbers of contributory desires, social and material, are cre- 
ated. 115 The creation of these desires, with the need for their satis- 
faction, leads to the creation of still others, and so the terrifically 
complex system of civilized desires arises. Modern inventions, 
such as steam engines, telephones, and phonographs, are made 



iisln much colder climates, as in the arctic region, conditions are still different. The 
extreme difficulty in satisfying contributory desires in those regions prevents their de- 
velopment. 



AFFECTIVE EXPERIENCE 329 

under the impelling force of sex desire, alimentary desire, and 
desire of preeminence on the part of the inventors, and still fur- 
ther complicates the system. There is no greater satisfaction of 
desires in civilization than in the primitive culture of virgin 
Samoa: probably far less! But we have been forced, and force 
ourselves, to satisfy the primitive desires in endlessly complex 
ways. 

In the general multiplicity of desires, it is impossible to dis- 
entangle the primary desires which enter into the different de- 
rived desires. It is clear, however, that in the vast majority of 
cases, our desires are derived from the primitive desire of the 
fifth, sixth, seventh and eighth classes. The food and rest de- 
sires, although satisfied with increasing difficulty, offer their chief 
difficulty in connection with problems of mating and supporting 
children, and it is the urge of the last two desires that multiply 
causes and the desire for them. In many cases, the desires for 
causal factors ultimately become engrossing, and "civilized" man 
is often so much occupied with the satisfaction of these that he 
does not mate at all, although he may have acquired the means to 
do so. The primitive sex desires have expended themselves in 
means, and the primary ends are ignored. 

Full discussion of the development of desires, and their func- 
tions, belongs to Social Psychology, which must ultimately be 
founded on the basis of desires and the satisfaction of desires. 

§8. Hedonic feeling. 

In the discussions of feeling in the past, pleasantness and un- 
pleasantness have received more attention than any other feel- 
ings, and have sometimes been treated as if. they were the only 
feelings. For this reason, the term "hedonic" has occasionally 
been applied to all feeling, although it properly describes pleas- 
antness and unpleasantness only. Pleasantness and unpleasant- 
ness together, as positive and negative aspects of the same fac- 
tor, have even been described as "characters of sensation," on 
the same plane as quality, intensity, etc. This characterization 
has, of course been abandoned. Hedonic feelings are a common 
accompaniment of sensory and thought content, but are by no 
means invariably present. 



330 ELEMENTS OE SCIENTIFIC PSYCHOLOGY 

Various causes have been ascribed to unpleasantness and 
pleasantness. Bringing somewhat divergent theories under one 
general form, we may say that the common view has been that 
pleasantness accompanies those reactions and organic conditions 
which have been in the past beneficial to the organism, and un- 
pleasantness those which have been harmful. Particular conditions 
which are actually harmful, such as the effects of certain drugs, 
are pleasant because they are conditions which in the past have 
been generally produced by beneficent stimuli or activities, and 
the organism has not adjusted itself to the effects of the newer 
stimuli and activities which produce, temporarily at least, the 
same conditions. Painful stimulations, such as operations on the 
nose and throat, which may be beneficial to the organism, pro- 
duce unpleasantness because in the remote past all most painful 
stimulations have produced harmful results, and practically none 
have produced beneficial results, and the organism has not ad- 
justed itself to the quite different conditions of modern surgery. 

There is, of course, a certain truth in this theory, but it does not 
express adequately the facts at the present time. It is perhaps 
more adequate to relate hedonic feeling to activities and organic 
conditions through desire. All activities which satisfy desires are 
pleasant, and all activities which inhibit or delay the satisfaction 
are unpleasant, that is, they produce the organic conditions (at 
present not definitely identified) which are experienced as 
pleasantness and unpleasantness. To this we must add that it is 
quite possible that certain types of activity which will satisfy pri- 
mary desires when the desires arise, may appear in the child be- 
fore the desire appears, and that these activities will produce 
pleasantness. This is, of course, involved in the basal conception 
of instinctive activities, which is that integrated reaction patterns 
appear in the animal antecendent to the conditions in which they 
may be fully exercised. Even if the play activities of the child 
should occur before the conscious desire for activity (we are not 
assuming this to be the case) these activities would produce 
pleasant feeling. We must add further that the laws of habit hold 
in regard to feeling, as in regard to all processes, and that there- 
fore activities which have become mechanical, the desires prima- 



AFFECTIVE EXPERIENCE 331 

rily connected with them having ceased to occur in them, may still 
be pleasant, if they were originally pleasant. 

The relation of "pleasantness" to "pleasure," and of "un- 
pleasantness" to "pain", has been the source of some confusion 
in the past. The terms pain and unpleasantness were, in the early 
history of psychology, used interchangeably, and so also were the 
terms pleasantness and pleasure. The later tendency was to dis- 
tinguish these terms sharply, using pain for the sensation, and un- 
pleasantness for the feeling: pleasantness for the feeling (simple) 
and pleasure for the emotion (complex, including pleasantness as 
one of its components). Since the distinction between sense data 
and feelings has necessarily been made less sharp of late, it may 
de doubted if the former distinction is useful. Unpleasantness 
seems to differ from pain in being less intense, and less distinctly 
localized: but we may well expect to find that otherwise the two 
states are the same. Even the "pain" resulting from stimulation 
of the skin in certain ways, seems indistinguishable from un- 
pleasantness when of low intensity. The distinction between 
pleasure and pleasantness may, perhaps, be more useful: pleasure 
may indeed include other elements than pleasantness, although 
it is at present impossible to say just what these other elements 
may be. 

§9. Observational and experimental work on feeling. 

Attempts to study feeling which have been made in the past 
may be classified under the three heads of genetic, introspective 
and experimental. 

(a) Genetic interpretation 

The genetic study has consisted of the observation of the reac- 
tions of children, and the attempt to interpret them in terms of 
emotions and simpler feelings experienced by adults. This method 
is, of course, valid, if we have an adequate knowledge of the adult 
feelings, and of the expressions (actions observable by another per- 
son) which definitely indicate the occurrence of these feelings. If, 
for example, we knew exactly what visible, or otherwise observ- 
able reactions in a normal adult human being indicate the occur- 
rence in chat individual of a definite feeling which we will agree 
to call fear: and if we should find those reactions occurring; in a 



332 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

chiM of a given age under given stimulus conditions, then we 
could say that the child under those conditions experienced fear, 
Unfortunately, the most essential reactions in a feeling of this 
kind are those (visceral) which are not directly observable except 
by the individual himself, and our knowledge of the other reac- 
tions (striped muscular principally) which invariably accompany 
these essential visceral reactions is far from adequate. On this ac- 
count, the genetic studies which have been made have resulted in 
little but confusion. In the most recent studies of this sort, 116 the 
reactions of children to various stimuli: auditory, visual, etc., 
have been carefully observed, and it has been found that infants 
are startled (show violent general contractions of the striped mus- 
cular system) when a loud, high-pitched sound stimulates their 
ears; and that they may cry. These observations are useful, and 
the results valuable for further reference when the actual results 
are set down without addition. But, unfortunately, it is further 
inferred that these infants experienced "fear," although the as- 
sumption is somewhat clouded by the "behavioristic" principle 
that one cannot speak of that which the person or animal under 
scrutiny experiences, but only of that which the observer experi- 
ences. The inference is at any rate made, that the infant has the 
total essential reaction which an adult has when he is commonly 
said to experience fear. 

Now we know that the general muscular reactions which were 
observed in these infants may be shown by an adult who is merely 
startled, and who has no fear in the usual sense of the term: 
and also that these general reactions and the crying reaction may 
be shown by adults in cases where there is neither startle nor fear, 
but merely pain. Hence we have no grounds for assuming, from 
these simple observations, the existence of fear in these infants at 
all. The observations are interesting studies of the behavior of 
infants under definite stimulation conditions, provided nothing is 
ascribed to them but that which is actually observed: but they 
do not bear on the problem to which they have been referred, nor 
do they give us as yet any important information concerning the 



us" Behavioristic " work is here classed as genetic. Behaviorism is, in fact, the later 
form of genetic psychology, its general methods being those of the earlier genetic 
school, with the addition of more precise use of apparatus. 



AFFECTIVE EXPERIENCE 33 



feelings of either adults or infants. This criticism may be ex- 
tended to cover all the genetic work which has been done on the 
problem of feeling. The genetic method can be usefully applied 
here only after we have acquired much more information on the 
subject of feelings than we now possess. 117 

(b) Introspective work. 

In the strict meaning of the term, all work on feelings must 
be fundamentally introspective, or must be based on thoroughgo- 
ing introspective observation, since the feelings are just those con- 
tents which can be observed only by the individual who has them, 
and who must therefore observe them by "looking into" his own 
organism. The term introspection has, however, come to have a 
different meaning, and does not signify observation through the 
somatic and visceral afferent neurons, but signifies apparently a 
peculiar method of observing objects of all kinds, whether through 
the external or the internal senses. Just what this method involves 
in theory, and the assumptions on which it is based, are not clear 
to those who do not belong to the "introspectionist school", but 
in practice, the method very often seems to come down to the ob- 
servation of all content, so far as possible, ivliich is present dur- 
ing* any given period of time. This method is sharply opposed 
to the experimental method, which always aims to narrow the ob- 
servation at any given time to a small group or detail of content, 
selected in advance for observation, withdrawing attention for the 
moment from all other content. 

Intro spectionist attempts to study feelings have resulted in con- 
siderable masses of observations on feelings, organic sensations, 
kinesthetic data and thought contents, but from all these detailed 
observations there are no conclusions obtained as to any general 
principles or facts of feeling. The observations remain mere his- 
tories of the different sorts of reports which different observers 
were able to make under different and similar conditions. This is 
perhaps the outstanding virtue of the introspectionist school in its 
work on feelings : that no general conclusions have been made. 

ii7The acquisition of data on the growth and development of children, as a purely 
1 ' behavioristie " or physiological study, is, however, of great importance, and as more 
information is obtained concerning the feelings, this data may become material for the 
application of the genetic method. 



334 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

(c) Experimental work. 

One of the hypotheses concerning feeling which was formed in 
the early history of the subject was that some feelings, especially 
pleasantness and unpleasantness, were directly connected with the 
dilation and contraction of the blood vessels. This hypothesis 
was formed even before the visceral hypothesis of the feelings was 
elaborated, bnt both Lange and Sutherland, in outlining the vis- 
ceral hypothesis, gave the chief role in all feeling to the blood ves- 
sels. Much experimental work has been done on this point, with 
disappointing results. It has been found that all changes in feeling 
are accompanied by changes in the distribution of the blood in 
soma and viscera, and changes in blood pressure: but it has also 
been found that similar changes accompany all conscious activity, 
and even reactions which are not conscious. This might be taken 
as indications that all reactions produce changes in feeling : a con- 
clusion to which all considerations predispose us. But no connec- 
tion has been found between any specific feeling or type of feeling 
and any specific change in the vascular system. Fear always pro- 
duces a rise in systolic blood pressure; but so do joy and strong 
interest. Painful states, and pleasurable states, may either pro- 
duce swelling or contraction of the arms and legs through increased 
biood supply to these members. Undoubtedly there are definite 
connections between feelings and vascular conditions, but the latter 
are so complex that no simple measurments will suffice to reveal 
them. Dilation of the capillaries in the arm, for example, may at 
one time be shown by increased volume of the arm, the blood be- 
ing forced into it because the blood-vessels of the viscera are con- 
stricted. Yet at another time, the same relaxation of the capillar- 
ies in the arm may be accompanied by decreased arm volume, be- 
cause the visceral blood-vessels are also relaxed. It is not to be 
supposed that the vascular line of experimentation on feeling is 
infertile, but rather that it needs to be more highly developed. 

More recently two interesting lines of experimentation have 
been opened up by Washburne and Cannon, and have been further 
worked upon by Carlson and other experimenters. It has been 
found by these experimenters that the exciting emotions produce, 
or are accompanied by, a marked increase in adrenin, the internal 
secretion of the adrenal glands ; and an increase in the blood-sugar 



AFFECTIVE EXPERIENCE 335 

(glycogen) which is secreted by the liver. The increased adrenin, 
as well as glycogen, has been experimentally found in cats which 
have been made to show signs of fear and rage by being threatened 
by dogs, and also in animals excited by pain, and by being bound 
in unusual positions, although without any painful stimulation. 
Increased glycogen has been found in human beings after various 
exciting experiences, such as playing or watching football, and 
even after taking college examinations. The finding of increased 
glycogen in healthy reactors is itself a proof of increase in adrenal 
secretion, since the glycogen increase is due to the stimulation of 
the liver by increased adrenin content in the blood. Adrenin has 
also the effect of increasing the sensitivity of muscle, and also of 
neutralizing the effects of fatigue products, or preventing their 
usual effects. In both ways adrenin facilitates muscular activity, 
as well as promoting those glandular activities essential for pro- 
longed muscular activity. The exciting emotions, therefore, may 
be understood as preparations for strenuous work. The phenom- 
enon of "second wind" is believed to be due to the effect of adrenin 
on fatigue toxins. 

Experiments on hunger have been made to test the hypothesis 
that hunger is dependent upon contractions of the empty or partly 
empty stomach. In these experiments, the reactor swallowed 
a thin rubber bulb, attached to a rubber tube, connected to 
a recording tambour, ■ writing on a kymograph drumj> so that 
the changes in pressure within the stomach may be recorded. 
These changes in pressure are due to breathing, to irregular 
changes in tension of the diaphragm and abdominal muscles, 
and to changes in the contraction of the stomach itself, but 
the changes due to the latter cause can be discriminated 
from the other changes. Some reactors have been found 
to experience "hunger pangs", or "hunger pains", which 
occurred rhythmically, with short periods of relief intervening. 
"When these reactors are allowed to record on the kymograph, by 
pressing a key, the onset and cessation of the "hunger pangs", it 
is found that the beginnings and ends of the pangs are almost si- 
multaneous with the beginnings and ends of the stomach contrac- 
tions. The contractions in typical cases last from twenty to forty 
seconds, with intervals between ranging from a few seconds to a 



336 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

minute or more. The whole series may last from six minutes to 
two hours and a half. 

From these observations it has been argued that hunger is 
caused directly by the contractions (or perhaps is the contrac- 
tions), of the stomach. This inference is unacceptable, however, for 
the following reasons: (I) Alcohol, in moderate quantities, inhibits 
the rhythmic stomach contractions completely (the quantity con- 
tained in an ordinary cocktail, or even a less amount inhibits the 
rhythmic contractions), but it does not, as a large number of per- 
sons can testify, inhibit hunger, although it may stop the " pains" 
of hunger. (2) During certain periods of starvation, by the 
methods of recording above described, hunger was found to be 
present when the contractions were absent. (3) Some reactors, 
who experience "hunger" in a definite form, never have the 
"pangs" or "pains" described by the reactors of Washburn and 
others. In these cases the hunger is a continuous state, quite com- 
parable to thirst in its rise and course. This hunger is not mere 
emptiness, faintness, nausea, or any of the other feelings which 
are often associated with it, nor is it "desire for food", but a dis- 
tinct feeling sui generis. In many cases, hunger is distinctly 
pleasant, and not combined with any unpleasant or painful feel- 
ing which might lead to its being called a "pain" or "pang". (4) 
Peristaltic contraction of the stomach occurs during digestion, and 
other contractions of a violent type occur in nausea; but hunger 
does not occur with these, although hunger, if long continued, may 
pass over into nausea. It is difficult to see how these contractions 
can differ so in effect if hunger is caused by contractions. 

The situation in the empty stomach during ' ' hunger pains ' ' may 
perhaps be illustrated by an experience which many persons have 
had, following a burn in the palm of the hand. If the burned area 
is mildly smarting, closing the hand strongly may cause a consider- 
able increase in pain, and relaxation is followed by temporary re- 
lief: but the pressure is not the primary cause of the smarting 
pain. 

The experiments of Washburn, Cannon, Carlson and others do 
show that hunger is probably a local condition of the stomach, 
which is intensified by stomach contractions, and made painful 



AFFECTIVE EXPERIENCE 337 

thereby in some cases; but they show also that the contractions 
are not the primary hunger or condition of hunger. 

These experiments so far suffer from lack of psychological 
analysis, leading to an identification of the characteristic hunger 
with the pain, or pain and strain, which accompany it in extreme 
cases. The hunger, strain, pain, emptiness, faintness, nausea, and 
desire for food must be clearly distinguished from each other, in 
final experiments. 

§10. Feeling and habit. 

It is clear now that feeling has two sources. It is in part the 
result of local or systemic changes of a general nature, and it is 
in part the immediate result of reactions. Pathological changes in 
any of the organs in which receptors terminate or in the organism 
generally may produce modifications in feeling: and so likewise 
may non-pathological changes such as those occurring in fatigue 
and the elimination of fatigue products. Broadly speaking, the 
basal condition of feeling is the condition of the somatic and vis- 
ceral tissues. The influence of these conditions is especially ob- 
vious in moods: but it is to be remembered that in all feel- 
ing, the systematic condition is just as influential. The effects 
of reaction are produced in the tissues in accordance with the con- 
ditions existing therein, and the capacities for changes dependent 
on those conditions. 

Independent of the reactions of the moment, there is a basal 
feeling-condition at any time. The reactions further modify this 
feeling condition, producing the relatively sudden changes which 
we identify as the beginning, or the cessation, of this or that spe- 
cific feeling. The reactions follow the universal laws of habit for- 
mation, and we find, therefore, a large factor of habit involved in 
the rise and fall of the feelings. We admit that from the indi- 
vidual's beginning there are certain inherent tendencies to re- 
spond with specific feeling-reactions to specific stimulus patterns: 
to have pleasure, through responses to certain stimuli, and pain 
through response to certain others: but we must also admit that 
these tendencies are continuously modified by experience. "VVe ac- 
quire tendencies to respond with pleasure to stimulus patterns not 
originally pleasurable : and we lose the pleasure response to other 
patterns which originally released that response. The same is true 



338 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

of all tlie feelings, simple and complex. In the total mass of feel- 
ing-response of the individual, there is very little that is really "in- 
stinctive": the original tendencies have been so recombined and 
modified by learning that the resultant reaction-patterns are as 
thoroughly "acquired" as any group of reaction-patterns in the 
organism. 

In regard to the greater number of the nameable emotions, 
this is so readily understood and so generally known, that little 
exposition is necessary. The tendencies to become angry, or afraid, 
or elated, or sad, upon this or that stimulus pattern, are admitted 
to be habits, fixed by recency, frequency and vividness, as are all 
habits. The importance of habit in the specifically sexual feelings, 
and in the various feelings in which pleasure and disagreeableness 
are the conspicuous elements is perhaps not so generally under- 
stood. But these, just as much as the first named feelings, are 
really matters of habit. Situations which arouse strong sexual 
desires, and the complex of attendant feelings, in one person, do 
not arouse the same feelings in another, although the second per- 
son may have just as strong feelings of this class under other cir- 
cumstances. Any person under the influence of habit formation, 
may come to have sexual feelings under circumstances in which 
he formerly did not have them. The ease with which sexual per- 
versions are formed, the striking effect of incest prohibitions, and 
the rapid changes in sexual tendencies in persons brought up un- 
der strict "moral" inhibitions when subjected to more "lax" con- 
ditions, are striking exemplifications of the importance of habit in 
this realm. 

The influence of habit in connection with the feeling complexes 
in which pleasure and unpleasantness are present is clearly indi- 
cated in the realm of aesthetic appreciation. 118 Color combinations 



iisThe quickly varying styles of women's attire present several interesting problems 
as to the relation of hedonic feeling to "principles of beauty' ' and to " conventions. ' ' 
It is evident that many women derive pleasant feeling from the wearing of costumes 
while they are "in style," which when "out of style" are admitted by these same 
women to be ugly. It is possible that "style" and "beauty" are completely divorced 
as regards the effect of costume on women, but the questions as to whether the effects 
of one may completely counteract the effects of the other: whether the two effects 
may coexist: whether generalized hedonic habits (principles of beauty) occur in 
woman's appreciation of her costume and ornaments; or whether only particularized 
habits (conventions) occur in this sphere, are yet to be answered. It has even been 
alleged that real aesthetic appreciation is an exclusively male function, and that 
women's appreciation of beauty is a matter of convention only. 



AFFECTIVE EXPERIENCE 339 

which in one decade are generally considered to be disagreeable or 
unpleasant, are in another decade considered "beautiful". Tone 
combinations which are disapproved often come to be approved. 
The rise of the music which includes much dissonance or discord 
illustrates the progress of habit formation in this field. Almost all 
hearers accustomed to the smoothly harmonic music of the older 
schools, whether popular music or music of the "better" grade, 
find at first the modern "good" music of the dissonant sort as well 
as the popular jazz which corresponds to it, quite disagreeable. 
But after such music has been heard repeatedly, it begins to arouse 
feelings in which satisfaction and pleasure are predominant. 



CHAPTER XVI 
THE EMPIRICAL SELF OR "ME" 

One of the most obvious distinctions in the content of experi- 
ence is the distinction between the self and the not self, between 
me and the remainder of the observable world. This distinction 
in the content must not be confused with the distinction between 
the content and the ego, I, or knower, and does not involve the con- 
ception of a "soul", or "spirit". 

In our survey of experience, we have found the content to be 
analyzable into sentienda, relations and feelings; and have found 
further that the distinction between feelings and sentienda is 
purely one of convenience. Unless we can find a me, or objective 
self sui generis which somehow accompanies, pervades, or is ex- 
perienced with these contents, we shall have to conclude that the 
known self is also composed of these same elements. Actually, 
no unique self-content is discoverable, and careful analysis shows, 
as we might expect, that the empirical self is a synthesis of all 
the sentienda and feelings which together make up the experienced 
organism. In other words: the fundamental "me" is the experi- 
enced body (soma and viscera), as it is experienced through the 
functions of my visceral, somatic and external receptors. This 
is the central self, or the central part of the self. But the total 
self includes more than' this mass of content and its interrelations: 
it includes also the relation of these contents to other, outer con- 
tents. Family relations, social relations, and business relations, 
for example, tend to become relations with the self, which, meta- 
phorically speaking, enlarges to include them. The self of another 
person is, for my experience, his body and its conduct in so far as 
I can experience it. My experience of your self is limited, there- 
fore, to the processes dependent upon my visual, auditory, olfac- 
tory and cutaneous receptors. I cannot perceive your feelings: 
that part of your self is your own private property in so far as 
perception is concerned. Yet even this privacy is a limited one, 

340 



THE EMPIRICAL SELF OR "me" 341 

for another person may, in certain cases, experience your feelings 
as thought-contents : L e, I may think of them. 

Even the perceptual sharing of your feelings with another ob- 
server is not inconceivable. If one of the afferent nerves whose 
peripheral terminals are in your arm muscle could be dissected 
out, and tne terminals transplanted into the biceps of another per- 
son, leaving the connection of the nerve with your spinal cord in- 
tact, you could have the feeling of this other person's muscular 
contraction. Through similar crossing over of autonomic afferent 
nerves from one person to another — a surgical operation which is 
conceivable, although perhaps not practicable — the one person 
might literally experience (perceptually) the feelings of the other. 
The impossibility of your actually perceiving the feelings, and 
hence the inner self, of another person is therefore not due to any 
strange difference between these contents and other contents, but 
solely to the arrangement of your receptors, which precludes their 
being stimulated by the other person's feelings. Your inability to 
experience another's self, as he experiences it, is no more myste- 
rious than your inability to perceive a landscape when your eyes 
ar ; 3 closed. 

The self of one individual, in so far as it is experienced by an- 
other individual, or in so far as it is estimated by another, is prop- 
erly designated the personality. There are, of course, other uses 
of the term, but this usage is customary and preferable. 

In the self, there are certain factors which are more important, 
more fundamental, than others. These essential factors are the 
ones most constantly present. Here we find the essential relational 
factors involved in the "me". It is the persistent presence of 
these self factors, amidst the more transitory external factors, 
which distinguishes them from these external factors and gives 
the more constant reference to the ego which characterizes the 
"me". We may get away from any of the external objects, but 
we never get away from or shut out the feelings of the body. The 
more adventitious feelings and bodily processes are fused with the 
more persistent mass because, no doubt, of their qualitative like- 
ness and spatial localization. These adventitious feelings, how- 
ever, are not felt to be the essential nature of the self, but changes, 



342 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

or modifications of the self. Or, we may say, they are certain 
phases, or aspects of the self. 

This view of the feelings and emotions as modifications of the 
self, although an empirical one, is essentially involved in the phil- 
osophy of Spinoza, who prefigured in his speculations the tlfeory 
of the emotions formulated two centuries later by James and 
Lange. 

Psychic individuality, or self -hood, therefore, means more than 
mere capacity for experience. It means the existence of a specific, 
although complex, content which is persistently present; which, 
although it changes its total character, changes slowly; and hence 
is the standard against which all other content is measured. The 
self forms accordingly the basis for the perceived continuity of 
the ever-changing content. Its rhythmic variations with the so- 
lar day and physiological condition serve as the clock of con- 
sciousness. When hungry, the idea of the normal steps for ob- 
taining food are brought up through normal association. In the 
morning, the recurring associations with the morning state of the 
self bring up the proper ideas for that time of day almost unfail- 
ingly. The intricate system of associative nexus which bind past 
experiences together and make our relatively orderly mental life 
possible might be supposed to be controlled in some other way, 
but as a matter of fact, they are controlled by the particular asso- 
ciations of this bodily self with the other factors in the manifold. 

The mass of habitually experienced content is the funda- 
mental self. Even habitually experienced thought content may 
become a part of the total self. "Asa man thinketh, so is he", is 
trite but largely true. But the habitual trains of thoughts are 
determined to a large extent by the feelings: and so in the healthy 
individual, the self, including all these factors, is a rather coherent 
mass of content. 

In many cases an apparently normal individual possesses a 
doable self. The church-going business man, for example, may 
really think admirable thoughts on Sunday, and these thoughts 
may be allowed to- find expression in suitable action. On other 
days he may think only of business, and his actions may be quite 
at variance with his Sunday doings. It is quite probable that in 
such a case he builds up a double set of affective or inner 



THE EMPIRICAL SELF OR " ME " 343 

selves, one of these selves being associated with each of the 
thought-complexes. The evidence for this assumption is found in 
the fact that his facial and bodily expressions change with his 
change of character, and give us reason to suspect more profound 
organic modifications. Certainly, he has two sets of emotional 
habits. He really is not a hypocrite, in an ethical sense, but is a 
diseased person: a monster with two selves. 

There are an indefinite number of possible principles of bifur- 
cation of the self, and these bifurcations may be incipient or 
thorough-going, that is, they may affect little more than the habits 
of thought, or may affect the mass of organic processes. A man 
may be pure-minded at certain times, and lewd at others; he may 
be a buoyant optimist and a downcast pessimist ; and so on ad in- 
finitum. And any of these divisions of self-expression, by the grad- 
ual formation of associations, may become a cleavage affecting 
practically the whole personality. In some cases there may be 
three of these fractional personalities, or even more. 

It is probable that none of us is completely free from the taint 
of divided selfhood: but most of us need not fear any disastrous 
developments. The dangerous cases are those in which one divi- 
sion of the self has long remained an inner core of feeling, with- 
out the outward associated expression. An individual, for in- 
stance, may give rein to the moral member of his team of selves, 
and allow the lewd side to express itself only at the infrequent 
times when he thinks he is safe from the observation of his 
associates. In such a case, some change in the bodily condition, 
deeply stirring the whole self, may give the "repressed" self its 
chance, and it may flare up, perhaps suddenly, and become dom- 
inant. In extreme cases the sets of ideas constituting the thought 
side of the previously dominant self, and the other groups of ideas 
associated with these, are completely lost, and hence the patient 
not only evinces a seemingly new personality, but actually loses 
the memory of years of his life. These sudden changes are called 
alterations of personality, and in the cases where there is repeated 
change from one personality to the other or others, the terms al- 
ternation of personality and alternating personality are applied. 



APPENDIX I 
MENTAL DEFICIENCY AND MENTAL DISEASE 

§1. Abnormal psychology and mental inefficiency. 

The detailed discussion of mental disease and mental deficiency 
belongs to the extensive topic of abnormal psychology and to 
psychiatry, not to an introductory text of general psychology. It 
is important, however, that the student of general psychology 
should have some conception of the nature of the diseases and 
deficiencies which are most commonly described, since he neces- 
sarily will meet with references to the names of these conditions, 
even if he does not study abnormal psychology. 

The classifications and descriptions of mental diseases are 
largely the work of psychiatrists, who officially deal with the care 
of mentally diseased patients. Unfortunately, there are many 
systems of psychiatry, differing much in their conceptions of the 
natures and origins of mental diseases, and in their classifications 
and descriptions. Hence we cannot present here a sketch which 
will represent a concensus of opinion of psychiatrists, but can 
merely present certain matters concerning which the differences 
of opinion are relatively small. We shall approach the subject 
rather from the point of view of abnormal psychology, which is 
primarily interested in the analysis of the abnormal mental 
processes, and in their comparison with normal processes. 

We may distinguish between normal and abnormal mental 
processes in either of two ways. First, we may consider the whole 
range of variations in some type of response, and measure the 
range of variations. We may, for example, measure the simple 
auditory reaction times of many men, and when we have obtained 
the average time for each man, we may find that these averages 
range from 90 sigma to 250 sigma. In such a group, Ave would find 
relatively few individuals with averages lying between 90 and 100, 
and relatively few averages between 220 and 250. We would find 
a somewhat larger number of averages between 100 and 110, a 
still larger number between 110 and 120, and further increases 

345 



346 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

with each decade until the maximum would be reached between 
140 and 150 perhaps ; from which point on, the numbers would be 
found to decrease. 

"We might then assume that a simple auditory reaction time 
between 140 and 150 is "normal," and that reaction times lying 
between 90 and 100 and between 220 and 250 are decidedly "ab- 
normal." The 90-100 group in this case would be designated as 
supernormal; the 220-250 group as subnormal. But from that 
point of view we would not be able to define sharply the limits 
between normality and abnormality. A reaction time of 120, for 
example, would be classed as "normal" or "abnormal" according 
as we should arbitrarily draw the dividing line. In general, we 
would define the "normal" as that which is of relatively frequent 
occurrence ; but ' ' relatively " is a vague term. 

Similar determinations might be made for accuracy of re- 
sponse; for speed and precision of learning; and for any other 
mental processes. After establishing norms for the total range of 
mental processes, we might, theoretically, construct from these 
norms the definition of the "normal mind." 

The use of the terms "normal" and "abnormal" in the way 
just described is of little importance or convenience. For practi- 
cal purposes the terms are employed in a different way. 

Since we are dealing in psychology with the adjustments of 
organisms, we distinguish those adjustments which are sufficiently 
efficient for the needs of the individual from those which are 
definitely inefficient, and call the first normal, the second abnormal. 
The distinction is therefore one which rests primarily on practical 
ends, and not on the psychology of the animal as an individual. 

The man whose simple reaction time to an auditory stimulus 
averages between 90 arid 150 sigma is sufficiently quick in adjust- 
ment for all the requirements of life. The man whose average 
lies between 200 and 250 is too slow for many requirements. The 
first man is therefore rated as "normal" in reaction time; the 
second as "abnormal." The exact limits between the normal 
and the abnormal must be decided on practical grounds. 

Abnormal psychology, as the term is broadly used, deals with 
adjustments which are abnormal in the practical sense. The field 
of abnormal psychology is broad, since every individual is at some 



MENTAL DEFICIENCY AND MENTAL DISEASE 347 

time abnormal in some of his responses ; and a great many indi- 
viduals are consistently abnormal in one or more respects. In a 
narrower sense, abnormal psychology deals with those abnormali- 
ties which are systematized, that is, which occur in character- 
istic groups. 

A systematic group of abnormal responses which is congenital 
is designated as amentia. Amentias are incurable. Other groups, 
which usually arise later than childhood are called mental dis- 
eases, among which are the dementias. Some mental diseases are 
intermittent in their occurrence; others become steadily worse; 
still others may disappear in the course of time. Psychiatry, in 
the strict sense, deals with the care of the patients suffering from 
these disorders, and the attempt to cure or alleviate them. 

Mental diseases are customarily classified as psychoses, and 
under this heading there are many systems of sub-classification. 
Certain diseases, which, from the psychologist's point of view are 
as "mental" as are any of the admitted psychoses — in fact, more 
emphatically mental in many respects — are classified by some 
psychiatrists not as mental diseases (psychoses), but as nervous 
diseases or neuroses. Strangely enough, these neuroses are pre- 
cisely those disorders (hysteria, neurasthenia, psychasthenia) for 
which no neurological bases or causes have been discovered or 
even strongly indicated. These diseases have therefore been 
further designated as functional neuroses, and contrasted with 
the psychoses which are assumed to be due to structural defects 
or degenerations in the nervous system, or to the effects of toxins 
or other chemical substances upon the nerve cells. 

The origin of this misleading terminology is complicated, 
being in part due to the old metaphysical theories concerning the 
mind ; in part to the fact that the neuroses are in general curable, 
while the other psychoses are not; and in part to the very fact 
that the assumed neural bases for the neuroses were not even 
conjecturally definite. 

Of late, there has been a tendency to drop the term "neurosis," 
and to classify all mental diseases as psychoses; and there has 
been also a variant tendency to substitute the term psychoneurosis 
or neuro -psycho sis for "neurosis." This latter tendency is un- 
fortunately confusing, since the term "psychoneurosis" has 



348 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

earlier had just the opposite meaning, namely, the psychoses 
exclusive of the so-called neuroses. 

It is practically useful to separate the psychoses from the 
neuroses in our discussion, while understanding that both names 
are without intrinsic significance, and that they might better be 
designated as " Group A" and " Group B." 

§2. The psychoses. 

Psychoses vary widely in degree of affliction, from those which 
are so light as to pass the ordinary observer unnoticed, to those 
which are so grave that they not only are noticeable to the average 
man, but require special care or restraint. To the latter type of 
case only is the term insanity properly applied, a patient not 
being insane, strictly speaking, so long as his trouble does not 
necessitate the taking of specific action towards it by other people. 

The typical psychoses, that is, those which occur in character- 
istic forms and have been definitely described, are: Dementia 
praecox, paraphrenia, paranoia, maniac-depressive psychoses, 
paresis or general paralysis, senile dementia, epilepsy, and 
various alcoholic and drug psychoses. Many variant forms of 
these diseases have been named and described by psychiatrists, 
but those above named are the types on which there is substantial 
agreement, although the agreement is far from complete. 

Senile dementia is a form of deterioration of response which 
occurs in old persons, usually not before the age of sixty. It may 
be described as an exaggerated form of the type of mental decay 
which commonly occurs in old age; but such description is not 
quite accurate. Senile dementia is characterized by a lowering 
of integration, and by a breaking down of many specific integra- 
tion tendencies previously established. Attention, for example, 
is not readily maintained, and does not reach a high level. Per- 
ceptions are inaccurate, and both illusions and hallucinations in- 
crease in frequency of occurrence and in disturbing power as the 
disease progresses. Loss of memory, and occurrence of false 
memories are important characteristics, and delusions (i. e. } sys- 
tematic false thoughts together with false perceptions of the 
environment), result. 

The delusions of senile dementia may take the form of belief 



MENTAL DEFICIENCY AND MENTAL DISEASE 349 

on the part of the patient that he is being persecuted ; or the form 
of groundless self accusation ; or of vast self-importance ; or one 
of many other forms. The patient is unable to learn, and has an 
exaggerated intolerance for new conditions and new ideas. Self, 
and the ideas of self, become unduly prominent and persistent, 
and normal reactions to other persons become lessened. These 
conditions we commonly describe as selfishness, egotism, and dis- 
regard for the rights of others. Customary restraints on the 
stronger habitual tendencies (as of sex) are lessened, resulting in 
attempts at rape, indecent exposure, and other antisocial actions. 
The patient may be extremely hard to manage until tendencies 
towards muscular weakness and nervous exhaustion induce a con- 
dition of helplessness. 

Dementia Praecox, sometimes called schizophrenia, may occur 
at any time of life, even in infancy, although characteristically 
showing itself near the period of puberty. It is characterized by 
hallucinations and illusions, but more fundamentally by emotional 
deterioration. Normal desires and interests, even those of sex, 
are weakened, and pride and ambition are lacking. The patient 
may fall into a state of profound apathy, or he may be very irri- 
table. Thought processes are erratic and illogical. Attention is 
impaired, especially in the apathetic cases. The retention of what 
has been learned before the onset of the disease is not affected, 
except in late stages of long standing cases. Further learning is 
however made difficult. 

Normal coordination of response is lessened in dementia prae- 
cox ; in other words, volitional and purposive acts become reduced 
in frequency, in speed, and in accuracy. There is a corresponding 
increase in uncontrolled automatic activity, such as grimaces, 
laughter, and other impulsive acts. Certain reflexes, such as the 
knee-jerk, may be heightened, although they are sometimes less- 
ened. One manifestation of the lowered integration, which is 
sometimes mentioned, is a tendency towards masturbation in the 
early stages of the disease, but this is also characteristic of the 
other dementias and of amentia. Eventually a condition of stupor 
may be reached, with the maintenance of fixed attitudes of the 
body and positions of the limbs. 

Paraphrenia is similar to dementia praecox, but develops later 



350 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

in life, usually in middle age. Its chief characteristic is the exist- 
ence of delusions which are well systematized. Paraphrenia 
passes through four well marked stages. In the first stage the 
patient is either emotionally depressed, or extremely irritable, 
with characteristic hypochondriac delusions of fictitious diseases. 
The second stage is paranoid, with delusions of persecution. In 
the third stage the delusions are of grandeur. The patient may 
identify himself with an important historical or allegorical per- 
sonage, such as Julius Caesar or the Pied Piper of Hamelin. The 
fourth stage is that of dementia proper (general mental ineffi- 
ciency, affecting memory, perception, attention and motor con- 
trol), but with comparative freedom from the delusions which 
mark the preceding stages. 

In paranoia there are highly systematized delusions, charac- 
teristically of persecution and grandeur, but with no other sig- 
nificant mental deteriorations. The patient does not, however, 
confuse his personality with that of some other person, but is 
thoroughly consistent. If he believes that he is a great inventor, 
he works persistently at invention. If he believes that he is a 
great religious teacher, he is active in religious propaganda. If 
he believes that an important lady is in love with him, he seeks 
persistently to make love to her, or to flout her, as the case may 
be. The delusion is, in short, an imaginative expansion of his own 
personality. 

The consideration of cases of paranoia sometimes leads theor- 
ists to believe that every serious advocate of something of which 
the theorist does not approve is "paranoiac." This results in 
two absurdities : all who have been responsible for advances in 
civilization are classed as paranoiacs, and the theorist is himself 
convicted of the same disease, through his taking his own beliefs 
so seriously. There is no real likeness between paranoia and de- 
votion to a cause, nor between paranoia and a reasonable belief 
in one's own worth. 

Melancholia and Mania are recurrent forms of mental disease ; 
that is, they are diseases which may occur periodically in the 
patient. These conditions are primarily emotional, but in their 
more pronounced forms they are accompanied by various per- 
ceptual and ideational defects: impaired accuracy of perception, 



MENTAL DEFICIENCY AND MENTAL DISEASE 35l 

of memory, and of judgment. In the most severe forms, hallucina- 
tions and delusions occur. 

Melancholia is emotional depression, in which the patient is 
lethargic, uninterested in his surroundings, and has lessened de- 
sires. The condition resembles the emotionally depressed type of 
the first stage of paraphrenia, but without the hypochondriac de- 
lusion of disease. Gloom possesses the patient, and his thoughts 
correspond to his emotional state, taking extremely pessimistic 
forms. His delusions take the form of sin, shame, and defeat. In 
mania, on the other hand, the patient is elated, excited, and in 
extreme cases delirious with joy, anger, or some other excited 
emotion. His thoughts are rapid and his words fluent, and his 
imaginative powers are at high tide. This is the "lunatic" of the 
popular conception ; the man who ' ' raves. ' ' 

Melancholia alone may recur periodically, with intervening 
periods in which the patient is apparently normal. Mania alone 
may also be recurrent in the same way. In other cases, mania 
and melancholia alternate, the patient passing directly from the 
one to the other. In still other cases there are normal or "lucid" 
intervals between the alternating abnormal phases. These latter 
forms constitute the true manic-depressive insanity. 

Manias and melancholias of non-periodic form may occur in 
alcohol psychoses, drug psychoses, or other psychoses of specific 
causation. These are not classified with the manic-depressive 
type. 

Paresis, dementia paralytica, or general paralysis of the in- 
sane, is a disease of fairly rapid course, beginning usually in 
middle age. It includes various disorders of sense perception, 
thought and attention, beginning sometimes with delusions of 
grandeur or of insignificance ; or with excitement, melancholia, or 
hallucinatory states. It progresses to disorders of memory, 
general motor incoordination, and muscular weakness, and ends 
in two or three years in the death of the patient. There are some- 
times definite attacks of paralysis resembling epileptic fits, but 
usually without convulsions. Hypochondriac delusions of sin and 
disease sometimes occur. 

Paresis is the one mental disease whose cause is definitely 



352 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

known. It is always a result of syphilis, beginning, in some cases, 
years after the syphilitic infection. 

Epilepsy is a disease characterized most strikingly by what 
are popularly called fits. For some hours, or even days, preceding 
a "fit," the patient may have warnings in the shape of emotional 
disturbances and disturbances of sense perception. He may be 
restless or excited or depressed or morose, or he may have fear 
or apprehension. He may have hallucinations of one or more of 
the senses. His imaginative processes may be unusually rapid 
and vivid. There may be jerking, trembling, or other uncontrolled 
movements of a few or many muscles. In many cases, immedi- 
ately preceding the "fit" there is a "warning" or "aura," con- 
sisting of a peculiar visceral or somatic feeling, sometimes 
accompanied by motor signs. 

The fit, in severe cases begins with strong contraction of the 
muscles and the patient falls unconscious. Sometimes he utters a 
shriek, or more often a gutteral cry. Then follows, after a few 
moments, a period of alternate relaxation and contraction of the 
muscles ; the patient bites his tongue, jerks his arms and legs, and 
contorts his body. Following this, the patient becomes quiet, with 
muscular relaxation, remaining unconscious for a varying time. 

There are lesser fits or seizures, in which the muscular signs 
are less severe, and the patient may not fall, although he may lose 
consciousness. In some cases, even the loss of consciousness does 
not occur; the patient is merely "dizzy" for a brief period. 

In other cases, the seizure takes the form of a complete loss 
of consciousness, with no definite external sign. During these 
" absences' ' as they are technically called, the patient may con- 
tinue automatically the details of his occupation, or may go 
through more complicated actions, even journeying some distance. 

In certain cases, the epileptic attack takes the form of violent, 
maniacal activity of a coordinated sort, in which brutal crimes 
may be committed. In still other cases, the seizure is a mood of 
great exaltation and pleasure, with vague delusions of grandeur: 
the "ecstasy" of the mystics. 

After many epileptic seizures the patient usually begins to 
show the perceptual and ideational symptoms of the dementias; 
but in his early history, he is "normal" in the periods immedi- 



MENTAL DEFICIENCY AND MENTAL DISEASE 353 

ately following recovery from the seizures. Nothing is definitely 
known about the cause or causes of epilepsy, although various 
theories have been advanced. 

In addition to the types of psychoses above described, there 
are various systematic mental abnormalities due to alcohol, mor- 
phine, and other drugs; and a group of "symptomatic psychoses" 
due to febrile conditions, over-activity or under-activity of the 
thyroid, parathyroid, and other ductless glands, and to diseases 
of other visceral organs. 

True psychoses are in general not curable, although some cases 
of manic-depressive insanity, and perhaps some of epilepsy im- 
prove under good living conditions. It is claimed, however, that in 
persons who have hereditary tendencies to mental disease, the 
development of the disease may be prevented by protecting the 
patients from trying and exhausting influences, if such protection 
is given before the abnormalities become established. 

The manic-depressive type of insanity, in persons predisposed 
to it, is apt to appear at times of emotional stress. Hence in 
women, the relative frequency of its appearance at the three 
emotional peaks of puberty, marriage, and childbirth. 

§3. The neuroses. 

The neuroses include a wide range of mental disorders, of 
which the well marked types are hysteria, neurasthenia, and psy- 
chasthenia. The neuroses, we assume, in accordance with the 
general assumption of the relation of mind to the organism, involve 
improper functioning of the nervous system, just as much as do the 
psychoses. But this is purely a psychological assumption and 
the neuroses must be considered from the strictly mental side, 
since no neural abnormality has as yet been found in these cases. 
There are many theories as to the causes of neuroses, and many 
and divergent types of medical treatment based on these theories. 
All of these forms of treatment have some success in alleviating 
the disorders; and none of them has such large success as to 
justify the belief that any general causal conditions have been 
discovered. 

Hysteria, or pithiatism, shows itself in various forms. In 
severe cases there are crises or "attacks," somewhat similar to 



354 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

the epileptic fits, but having a much wider range of variation. 
The patient may become cataleptic, i. e., have muscular rigidity 
without falling, and may maintain a fixed attitude for a long 
period of time. Or he may exhibit various movements, sometimes 
of a highly excited sort. Hysterical laughter is but one type of 
such movements. 

In many cases there are not definite crises; but there are 
various abnormal reaction tendencies, called stigmata, present in 
all cases. 

The stigmata of importance all fall under the general head of 
dissociation, or fragmentary integration. The various units of the 
nervous system function normally as units, but some arcs function 
without being integrated into the general system. On the per- 
ceptual side this causes anesthesias of various sorts : anaphias, 
anacusias, athermias, analgesias, and anopsias. A certain part 
of the retina, for example, may be anopsic ; then the patient can- 
not see anything the image of which falls on that part of the 
retina ; yet stimuli to that part of the retina may produce definite 
response movements which are apparently unconscious. An ex- 
treme illustration of this sort of anesthesia is furnished by the 
patient of Janet who was apparently anaphic and analgesic over 
one-half of her body. She could not perceive pain or tactual im- 
pressions on that side, yet when instructed to say "yes" if she 
felt a pinch, and "no" if she did not feel it, she responded "no" 
every time she was pinched on the ' * anesthetic ' ' side, although her 
eyes were closed and she had no warnings but the pinches them- 
selves. 

The anesthetic areas, on skin or retina, in hysteria, are not 
really functionless ; and these areas are variable, an area which is 
anesthetic at one time being normal at another. In other words, 
the afferent nerve current from these areas is sometimes included 
in the general nervous integration, sometimes not. In some cases, 
the behavior of the patient seems to indicate that the neural tran- 
sits which are not integrated with the general system, are inte- 
grated with each other in a smaller system. 

Amnesias also occur in variable ways in hysteria; what is 
forgotten at one time may be remembered at another. In the case 
of hysterical amnesias, the neural mechanisms for the recall are 



MENTAL DEFICIENCY AND MENTAL DISEASE 355 

not absent; it is possible that the recall-transits may even occur, 
but are not integrated with the general system. In cases in which 
perhaps a second, lesser, integration system is set up, it may in- 
clude thought-processes as well as perceptual processes. 

There are many other characteristics of hysteria. The patient 
is easily hypnotized; he is subject to hallucinations of a vivid sort; 
but not to delusions of a systematic sort. Of the actual causes of 
hysteria we know nothing past dispute. 

Neurasthenia, or "nervous exhaustion" is marked by a con- 
stant feeling of fatigue, and by diminished energy, and diminished 
resistance to depressing factors of the environment. There is in- 
creased tendency for the arousal of unpleasant feeling by sensory 
stimulation, hence the patient shrinks from loud sounds, bright 
lights, etc. The sensory mechanism is not hypersensitive, but the 
feeling effect is abnormal. Attention is affected, not by decrease 
in the relative integration at any moment, but by increased varia- 
bility, so that sustained attention is difficult, and the integrations 
are subject to disturbance by slight sensory stimulations ; in other 
words, the patient is easily distracted. Hence, he learns with 
difficulty, and quickly forgets what he learns. Insomnia and 
digestive disturbances are usual features of neurasthenia. The 
emotional moods tend towards depression and melancholy. There 
is no fragmentary integration as in hysteria, and no tendency to- 
wards delusions or hallucinations. The failure of previously 
established muscular coordinations characteristic of dementia- is 
not present in neurasthenia. Cure is possible, through rest, 
proper nourishment, and relief from strain and worry. 

Psychasthenia is a neurosis which is more serious than neuras- 
thenia, and is characterized by excessive fears (phobias) and 
obsessions, with feelings of failure, inadequacy, and hopelessness. 
Sometimes the patient feels that the whole environment is unreal. 
The phobias take the form of fear of darkness, fear of disease 
or of death, fear of the opposite sex, etc., and are persistent and 
gripping. 

Hypochondria, a form of which has been indicated above as 
characteristic of the early stage of paraphrenia, has been de- 
scribed by some psychiatrists as occurring in independence of 
other psychoses, and is therefore in most cases classed as a neu- 



356 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

rosis. These cases are characterized in their early stage by ab- 
normal vividness of visceral consciousness, usually including the 
contents of aches, burnings, crawlings, and other disagreeable 
conditions of various organs, although physical diagnosis shows 
no affections of the organ concerning which the hypochondriac 
complains. The patient often believes that he has some disease, 
or combination of diseases, responsible for his disagreeable ex- 
perience; or he fears excessively the contracting of disease, of 
catching cold, etc. He is afraid to drink, dreading germs in the 
water ; he is afraid of kissing for similar reasons. Some patients 
keep detailed records of their symptoms : others read extensively 
in medical accounts of the diseases which they fear. Others in- 
dulge freely in patent medicines, chiropractic and other mechani- 
cal treatment, or in psychoanalysis and other "mental cures." 

In the course of time, the bodily functions of hypochondriacs 
do show pathological changes. The skin may become dry, or ex- 
cessively moist : constipation or urinary troubles become chronic : 
sexual impotence or irritability becomes chronic ; or the secretions 
of the glands become excessive or scanty; and so on. How far 
these effects are results of the long continued mental process ; and 
how far the mental processes are due to the physiological in the 
first place, medical diagnosis is not sufficiently refined to deter- 
mine. 

§4. Amentia, or mental deficiency. 

■ In addition to the individuals who are mentally diseased, who 
are either psychotic or neurotic, there are individuals who are 
classed as mentally deficient, or feeble minded. These persons 
are commonly assumed to have been defective from the earliest 
stage of infancy in which the individual can be adequately exam- 
ined. They are thus distinguished roughly from the mentally dis- 
eased, who are, in typical cases, those who have been at one time 
"normal," and have undergone deterioration. Amentia, there- 
fore, may be described as congenital, whereas mental disease is 
acquired. This distinction should not be strongly stressed, how- 
ever, since psychoses, and probably neuroses, are based on inher- 
ited tendencies or dispositions, or defects, and in the case of 
amentia, it is strictly speaking the constitutional defect or disposi- 
tion that is inherited, not the amentia, which is only the functional 



MENTAL DEFICIENCY AND MENTAL DISEASE 357 

expression of the fundamental defect. Nor should we stress much 
the difference due to the early appearance of amentia, and the 
delayed appearance of mental disease. The typical psychoses 
sometimes appear in early infancy, and perhaps neuroses may 
also. Until we have much fuller knowledge of the causes of the 
predispositions to amentia and mental disease, the distinctions 
must remain on the rough practical basis, and even so, cannot be 
made very clear to those who have not actually worked with the 
cases of various types. 

The responses of the feeble minded are in some respects like 
those of children of lesser years, and hence in practical classifica- 
tions these defectives are often rated in terms of the ages of nor- 
mal children. A defective person whose responses, when meas- 
ured or estimated by some standard, are found to be like those 
of a normal child of six years, is then said to have a "mental age" 
of six. Defectives who are chronologically 16 years or over and 
who have "mental ages" between 8 and 12 are commonly called 
morons; those having "mental ages" from 3 to 7 are called 
imbeciles; and those having "mental ages" of 2 or less are classed 
as idiots. 

Morons have been described as able to earn their livings under 
favorable circumstances, but not able to manage their social and 
economic affairs without direction and assistance. Imbeciles are 
described as able to carry out only the simplest tasks, and then 
only under constant supervision. Idiots can do little more than 
walk and feed themselves. Binet and Simon described idiots as 
unable to talk ; imbeciles as unable to learn to read and write ; and 
morons as unable to think (effectively). 

All such classifications must be considered as tentative and 
suggestive rather than as final and exact. Further, it must not be 
supposed that a defective who is classed as of the "mental age" 
of 8 is really in the mental condition of a normal child of 8. A 
child whose actual age (chronological age) is 12, and whose "men- 
tal age" is 8, may not differ very much mentally from a normal 
child of 8 ; but the mind of a man the actual age of 21, and "mental 
age" of 8 differs very much from that of a normal 8 year old 
child. All that is meant by the "mental age" rating of defectives 
is that in a certain standardized test or tests, the defectives attain 



358 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

the ratings which normal children of the ages specified would 
attain in that test. 

The differences between the mentally defective and the normal 
individuals are commonly referred to as differences in intelligence, 
and the tests employed are designated as intelligence tests. "In- 
telligence," so used, means general efficiency of mental life, includ- 
ing effective integration and ability to learn. The intelligence 
tests employed are of various sorts, ranging from problems in 
arithmetic and logic down to the ability to make change in money 
and point to the eye and nose. The assumption in such tests is 
that all the individuals tested have been given the same chances 
to learn the process in which they are tested, and hence, that the 
amount they have learned measures the relative intelligence. It 
is obvious, therefore, that training must always be taken into 
account, and that in the cases of children, great skill and under- 
standing of child psychology are required of one who should ad- 
minister the tests with success. 

In relatively few cases are the proximate causes of mental de- 
ficiency known. In some cases the secretion of the thyroid gland 
is insufficient; in some cases there are definite brain defects. In 
still other cases adenoids are the immediate cause of the defect. 
Defects of hearing and of vision are frequent causes of mental 
deficiency because they prevent learning. But in the great major- 
ity of cases the senses are normally efficient, and there is no de- 
fect in structure or function of the nervous system or the glands 
which can be shown in physical examinations. Yet the nervous 
system, in such cases, obviously does not function properly. As- 
sociations are formed with difficulty, and perceptual reactions 
modified but slowly. Somatic and visceral contents apparently 
receive more attention in the feeble minded than in the normal 
individuals. It almost seems that in the lower grades of mental 
deficiency the relations of external and organic perception are the 
reverse of those in the normal individual ; that the feeble minded 
person is primarily conscious of his body, the outer world being 
but a confused background against which organic processes viv- 
idly appear. 

The neural troubles of the mentally defective may therefore 
be summed up as defects of integration. These defects are ap- 



MENTAL DEFICIENCY AND MENTAL DISEASE 359 

parently hereditary, following the same laws of transmission from 
parents to children as do eye-color, teeth, and other physical char- 
acteristics. The defects are incurable, and hence those who are 
definitely feeble minded should not be allowed to propagate their 
kind. The individuals themselves may be made to learn by special 
training more than they would if left to ordinary school treat- 
ment; but this does not raise the intelligence of their children, 
although it may unfortunately enable them to marry and beget 
children. 

The foregoing sketch includes only those mental diseases which 
have been generally recognized, which are relatively frequent in 
their occurrence, and concerning which there is a considerable 
amount of agreement among psychiatrists. In addition, there is a 
long list of pychoses and neuroses which have been described by 
different psychiatrists. Some of these diseases are rare, some are 
vaguely defined, and some are recognized only by certain schools 
of psychiatry. Some are merely sub-types of the general diseases 
we have described. There are also a number of specifically nerv- 
ous diseases, such as chorea (St. Vitus' dance) and tabes dorsalis 
(locomotor ataxia), which have minor or secondary mental symp- 
toms and effects. 



APPENDIX II 
SOME USEFUL REFERENCE BOOKS 

This list includes books only. Reference to periodical litera- 
ture should be sought in the Psychological Index (issued annually) 
and the reviews and summaries in the Psychological Bulletin 
(monthly). There are certain topics mentioned in the text on 
which no book references are given, although many books have 
been published, because those books are useful only to the well 
grounded and critical psychologist, who can sift a bushel of chaff 
from a grain of wheat. Certain other topics are omitted from the 
references merely because they are technical and remote from the 
general purpose of the text. 

I. Psychological texts which present the subject from points of view significantly 
different from that of this text. 
Breese, B. B. : Psychology. 1917. 
Calkins, M. W. : A First Book in Psychology. 1910. 
James, W. : Principles of Psychology. 2 vols. 1890. 
Judd, C. H. : Psychology : General Introduction. 2d ed. 1917. 
Ladd and Woodworth: Elements of Physiological Psychology. 1911. 
Titchener, E. B.: A Textbook of Psychology. 1919. 
Watson, J. B.: Psychology from the Standpoint of a Behaviorist. 1919. 
Warren, H. W. : Human Psychology. 1920. 

II. Anatomy, physiology and psychobiology. 

Dunlap, K. : An Outline of Psychobiology. 2d ed. 1920. 

Greenwood, M. : The Physiology of the Special Senses. 1910. 

Herrick, C. J. : Introduction to Neurology. 1915. 

Howell, W. H. : A Textbook of Physiology. 6th ed. 1915. 

Luciani, L. : Human Physiology (transl. by Welby). 5 vols. 1911-17. 

Schaf er, E. A. : Text Book of Physiology. Vol.2. 1900. 

Schafer, E. A.: The Endocrine Organs. 1920. 

Starling, E. H. : Principles of Human Physiology. 3d ed. 1920. 

Quain's Anatomy: 11th ed. 4 vols. 1908. 

III. The Cranial Senses, 
(a) Taste and smell. 
Collet: L'odorat. Paris, 1904. 

Haycraft, J. B. : The sense of taste. The sense of smell. (In Schafer 's Text- 
book of Physiology). 

360 



SOME USEFUL REFERENCE BOOKS 361 

Henning, H. : Der Geruch. Leipzig, 1916. 
Hollingworth and Poffenberger : The Sense of Taste. 1917. 
Marchand, L. : Le Gout. Paris, 1903. 
Sternberg, W. : Geschmack und Geruch. Berlin, 1906. 
Zwaardemaker, H. : Die PJtysiologie des Geruchs. Leipzic, 1895. 
(See also tables of contents of books in list II.) 

(b) Audition. 

Hamilton, C. G. : Sound and Its Belaton to Music. 1912. 

Helmholtz H. von: On the Sensations of Tone (transl. by Ellis). 4th ed. 1912. 

McKendrick and Gray: The ear. (In Schafer's Textbook of Physiology). 

Miller, D. C. : The Science of Musical Sounds. 1916. 

Pole, W.: The Philosophy of Music. 1910. 

Watt, H. J.: The Psychology of Sound. 1917. 

Watt, H. J.: The Foundations of Music. 1919. 

Wood, H. J.: The Physical Basis of Music. 1913. 

Zahm, J. A.: Sound and Music. 1892. 

(See also tables of contents of books in list II.) 

(c) Vision. 

Burch, G. J.: Physiological Optics. 1912. 

Edridge-Green, F. W.: The Physiology of Vision. 1920. 

Greenwood, M. : Studies in special sense physiology. (In Hill's Further Advances 

in Physiology.) 1907. 
Helmholtz, H. von: Handbuch der Physiologischen Optik. 3d ed. 3 vols. 1910. 
Parsons, J. H. : An Introduction to the Study of Color Vision. 1920. 
Rivers W. H. R. : Vision (in Schafer's Textbook of Physiology). 

(See also tables of contents of books in list II.) 

IV. The dermal, somatic and visceral senses and feelings. 
Braun and Friesner: The Labyrinth. 1913. 

Cannon, W. B. : Bodily Changes in Pain, Hunger, Fear and Page. 1915. 
Carlson, A J. : The Control of Hunger in Health and Disease. 1916. 
Crile, G. W. : The Origin and Nature of the Emotions. 1915. 
Darwin, C. : The Expression of the Emotions in Man and Animals. American ed. 

1870. 
Harvey: The Feelings of Man. 1914. 
Head, H. : Studies in Neurology. 2 vols. 1920. 
Hertz: The Sensitivity of the Alimentary Canal. 1911. 

James, W., and Lange, C. G. : The Emotions (Psychology classics, vol. I). 1922. 
Mosso, A.: The mechanism of the emotions (Appendix to Goddard, Psychology 

of the Normal and Subnormal) . 
Mosso, A.: Fear (transl. by Lough and Kiesow). 1886. 
Mosso, A.: Fatigue (transl. by Drummond). 2d ed. 1906. 
Shand, A. F. : The Foundations of Character. 2d ed. 1920. 
Sherrington, C. S. : Cutaneous sensations. The muscular sense. (In Schafer's 

Textbook of Physiology.) 
Ribot, Th. : The Psychology of the Emotions. (Contemp. sci. ser.) 1897. 

(See also tables of contents of books in list II.) 



362 ELEMENTS OF SCIENTIFIC PSYCHOLOGY 

V. Experimental methods and mental measurements. 

Franz, S. I. : Handbook of Mental Examination MetJwds. 2d ed. 1919. 

Stern, L. W. : The Psychological Methods of Testing Intelligence, (transl. by 

by Whipple). 1914. 
Terman, L. M. : The Measurement of Intelligence. 1916. 
Titchener, E. B.: Experimental Psychology. 4 vols. 1915. 
Whipple, G. M. : Manual of Mental and Physical Tests. 2d ed. 1914. 
Yerkes, E. M. : A Point Scale for Measuring Intelligence. 1915. 

VI. Instinct and habit formation. 

Drever, J.: Instinct in Man. 1917. 

Colvin, S. S. : The Learning Process. 1911. 

Ebbinghaus, H. : Memory (transl. by Ruger and Bussenius). 1913. 

McDougall, W.: Social Psychology. 16th ed. 1921. 

Pyle, W. H. : Psychology of Learning, 1921. 

Watson, J. B.: Behavior. 1914. 

Thorndike, E. L. ; Educational Psychology. 3 vols. 1914. 

VII. Mental diseases. 

Bridges, J. W. : An Outlioie of Abnormal Psychology. 1919. 

Church and Peterson: Nervous and Mental Diseases. 1908. 

Diefendorf, A. R. : Clinical Psychiatry. 1912. 

Dercum, F. X. : Clinical Manual of Nervous Diseases. 1914. , 

Janet, P.: The Mental State of Hystericals (transl. by Carson). 1901. 

Janet, P. : The Major Symptoms of Hysteria, 1907. 

Goddard, H. H. : Feeblemindedness, Its Causes and Consequences. 1914. 

Rosanoff, A. J.: Manual of Psychiatry. 5th v ed. 1920, 

Seavill T. D. : Clinical Lectures on Neurasthenia. 4th ed. 1908. 

Tredgold, A F. : Mental Deficiency. 2d ed. 1915. 

Miner, J. B. : Deficiency and Delinquency. 1918. 

Hollingworth, Leta : The Psychology of Subnormal Children. 1920. 



INDEX 



A 

Absolute pitch, 151 
Accommodation, 266 
Action pattern, 189 
Acuity, auditory, 1-18-9 

tactual, 152-3 

visual, 135, 136-8 
Acumeters, 148-9 
Adaptation, gustatory, 52 

olfactorv, 55 

visual, 70 ff., 139 
Adjustment, {see Reaction) 
Adrenin, in emotion, 334-5 
Affection, 312 ff. 
After-images, 69 

negative, 71 
Age, mental, 357 
Algesimeter, 153 
Algometer, 153 
All-or-none law, the, 115 
Amentia, 347, 356 ff. 
Amnesia, hysterical, 354-5 
Ampullar sense, 108-9 
Anacusia, 93 
Anaglyphs, 268 
Analgesia, 104 
Anesthesia, hysterical, 354-5 
Anger, 320 

Anticipation, 161, 194 
Anosmia, 55 
Anosphresia, 55 
Appetite, 106 

sexual, 107 
Approval and disapproval, 316-7 
Arc, reaction, 177, 183-4, 186 ff. 

{see also Reaction) 
Aristotle's illusion, 292-3 
Association of ideas, 299, 304-6 

mediate, 306-7 
Assent, 195 
Astigmatism, 135-6 
Ataxia, 102 

Attention, 202 ff., 224-5 
Audition, 80 ff. 

Auditory perception, physiological hy- 
pothesis, 91 ff. 
Autonomic system, 179, 181-3, 314-5 
Aversion, 194, 325, {see also Desire) 
Awareness, 22, 24, 25, 116 {see also Con 

sciousness) 
Axon, 177 
Axon-reflex, 178 



B 

Beats, 88, 89, 90 
Betweenness, 122, 129-30 
Binet's letter square, 168 
Binocular disparity, 267-9 
Blood cells, 174 
Brain-stem, 180 
Breathing, 198 
Brightness, 39 

C 

Catalepsy, 354 

Cell, the, 172 

Cerebrum, 180 

Character analysis, 256 ff. 

Character, of sense data, 39, 112-120 

Chiaroscuro, 269 

Chromatin, 172, 185 

Circulation and feeling, 334 

Color blindness, 75 ff. 

Color induction, 72 

Color mixing, 73 

Color names, 56-57 

Color vision, defects of, 75 ff. 

Hering's theory, 79 

Ladd Franklin Theory, 80 

measurement of, 146-7 

physiological hvpothesis, 67, 68 

tests of, 143 ff" 
Color weakness, 78 
Colors, complementary, 60 

primary, 56 

number of, 57 
Complications, 37 
Conation, 323 ff. 
Conception, 163 
Connective tissue, 175 
Consciousness, 22, 24, 25, 32, 197, 202 

and instinct, 219 ff. 

as a social product, 206 

conditions of, 36 
Consent, 196 
Continuation images, 67 
Content, 24, 116 

indefinability of, 29 
Crises, hysterical, 353-4 
Contractions of stomach, 105 
Contrast, color, 72 
Convergence, 264 
Corresponding points, 264 
Cortex, of the cerebrum, 184-5 
Critical frequency, 1 



363 



INDEX 



Critical points, 129 
Currents, efferent, 48 
Cytoplasm, 172 



D 



Data, of sense, 37 



Decision, 195 
Deficiency, mental, 356 If. 
Degree of consciousness, 202, ff. 
Deja-vu, illusion of, 161-2 
Deliberation, 195 
Delusions, 348, ff. 
Dementia paralytica, 351-2 

praecox, 349 

senile, 348-9 
Dendrite, 177 

Depression and elation, 320 
Depth perception, 263 ff. 
Dermal senses, the, 95 ff. 
Desire, 194, 195, 196, 323 ff. 

and pleasure, 350 

habit formation in, 326-9 
Deuteranopes, 75 ff, 146-7 
Dichromats, 76, 147 
Difference thresholds, 124 ff. 
Difference and identity, 124 

brightness, 139 ff. 

pitch, 150-1 

saturation, 143 

tactual, 153 

tone, 142-143 
Difference tones, 88 
Discord, 90 
Discrimination, 244 ff. 

spatial, and reaction, 261 
Diseases, mental, 347 
Dissonance. 90 
Dizziness, 286 

Dominance in integration, 208 
Doubling of visual objects, 265 
Drainage, 211 ff. 
Dualism, 33 

Dunlap's illusion, 296, 297 
Duration, 39, 117 

E 

Ecstacy, 352 

Effectors, 47, 76 

Ego, 24, 25, 26, 341 

Embryo, the, 73 

Emotions, and feelings, 318 ff. 
adrenin in, 335 
and learning, 225-6 
and visceral activities, 201 

Emptiness, 106 

Environment, 21 

Epilepsy, 352-3 



Episkotister, 141 

Equilibration, 287 

Errors, elimination of in learning, 237 

Esthesiometer, von Frey's, 151 

two-point, 152-3 
Esthesiometry, 151-2 
Esthetics, 18 
Evidence, anecdotal, 32 
Exhaustion, 109 
Experience, 23, 29 
Experimental methods, 31 
Exteroception, 42 

Eye movements and visual anesthesia,. 
288-90 



Fascia, 175 

Fatigue, 55, 109, 111 

Fear, 319, 332 

Fechner's formula, 127-128 

Fechner's weights, 159 

Feeble minded, the, 356 ff. 

Feeling, and accuracy of perception, 252 

and emotions, 318 ff. 

and habit formation, 337-9 

and illusion, 251 

and learning, 225-6, 227 

and reaction, 314 ff. 

experimental work on, 334-7 

genetic interpretation of, 331-3 

introspectionist work on, 333 
Feelings, 312 ff. 

cardiovascular and respiratory, 107-& 

choking, 107 

depression, 107 

driving force of, 321 ff. 

essential characteristics of, 313-14 

excitement, 107 

fatigue, 109-111 

genitourinary, 107 

giddiness, 109 

nausea, 105, 106, 336 

relief, 108 

sexual, 101, 107 

sharing of, 341 

simple, 315 

stuffiness, 108 

suffocation, 108 
Fertilization of egg, 173, 183 
Fits, 352 
Flavors, 54 
Foetus, the, 173 
Foreshortening, 273 
Frequency, 224, 237 
Fullness, 106, 316 
Fusions, 37, 38 

of dermal sentienda, 99 

gustatory, 51 



INDEX 



365 



Fusions — Cont 'd. 
olfactory, 54 
visual, 58 ff. 



G 



Galton's whistle, 150 
Germ cells, 174, 185-6 
Germ layers, the, 173 
Gland cells, 48 
Glands, 175 

reaction of, 199 ff. 
Gustation, 50 ff. 

H 

Habit, 210 ff. 

Habit formation, 223 ff. 

and feeling, 337-9 

in desire, 326-9 

rhythmic, 342 
Habits, implicit, 227-30 
Hair cells, 172, 179, 181 
Hallucination, 115-116 
Haptometer, 153 
Harmony, 90 
Hedonic feeling, 329 ff. 
Heredity, 172, 185-6 
Hexahedron, color, 61 
Holmgren's test, 144 
Hunger, 195, 335-7 
Hyperopia, 135-6 
Hypochondria, 350, 355-6 
Hypotheses, scientific, 28-32 
Hysteria, 353-5 



Ideas, 162 ff. 

innate, 223 
Idio-retiral light, 79, 116 
Idiots, 357-8 

Illumination, unit of, 139 
Illusion, 246 ff. 

of motion, 109, 291 

of rotation, 286 

spatial, 291 ff. 
Images, 158, 162 ff. 
Imagination, 156 ff. 

cultivation of, 168 

productive, 157, 158-60 

reproductive, 156-7, 158-60 
Imbeciles, 357-8 
Inefficiency, mental, 345 ff. 
Initiative reaction, 193 
Infra-red, 63 
Insanity, 348 

manic-depressive, 351, 353 
Instinct, 210 ff. 



Instincts, 214 ff. 

classification of, 217 ff. 

incomplete, 215 
Integration, 202 ff., 209, 208 ff. 

in amentia, 358-60 
Intelligence, 219-20, 358 
Intensity, 39, 115 

Interconnections, cerebral, 184, 204 
Intermediacy, 129-130 
Interoception, 42 
Intervention (visual), 269 
Introspection, 27-28 
Irradiation, 117-118 
Ishahara's test, 145 
Itch, 99 
Intuition, 314 



Jastrow's illusion, 295, 297 

J. H. U. test (for color vision), the, 145 

Jennings' test, 144 

Judgment, 308-11 



Kinesthesis, 101-102 
Knee-jerk, 190, 191, 192 
Konig's cylinders, 149-150 



Language and thought, 303-4 
Lag, of visual stimuli, 68-69 
Learning, 211 ff., 223 ff., 197 

elimination of 
error in, 237 

instructions in, 232-3 

limits of, 226-7 

new responses, 230-5 

role of feeling in, 322-3 

specific problems of, 230 ff. 

serial, 235-7 
Local sign, 118-119 

M 

Magnitude, 122 

Mania, 350, 351 

Matter, 24 

Maxwell's discs, 73, 142, 143, 147 

McLougall's list of instincts, 218 

Meaning, 254JL 

Me, the, 341 ff. 

Measurements, auditory, 148 ff. 

gustatory, 132-133 

mental, 19 

of absolute pitch, 151 

of color vision, 146-7 

of dermal sensitivity, 151 ff. 



366 



INDEX 



Measurements — Cont 'd. 

olfactory, 132, 134 

sensory, 131 ff. 

visual, 135 ff. 
Mechanism, bodily, 170 ff. 

sensory, 47 
Melancholia, 350, 351 
Memory, 160 
Mental measurements, 19 
Mind, 20, 23, 27 
Mind reading, 239 
Modality, 40 

Modes of imagination, 157-8 
Moods, 319 ff. 
Morons, 357-8 
Motor centers, 184-5 
Movements, perception of, 119-120 
Miiller-Lyer 's illusion, 296, 297 
Myopia, 135-6 
Muscle cells, 47 

Muscle, structure and function, 175-6 
Muscular activity and thinking, 300 ff. 



N 

Nagel's test, 144 
Nausea, 105, 106, 336 
Nela test, 146 
Nerves, 180 

Nervous system, the, 179 ff. 
Neural pattern, 189 
Neurasthenia, 355 
Neurons, 176 ff. 

function of, 177-8, 205-6 
Neuroplasm, 172 
Neuroses, 347, 353 ff. 
Neutral zone, 76 
Noises, 80 

Normality, conception of, 345-7 
Nucleus, of cell, 172 



O 

Objects, physical, 24 

of sense, 33 
Observation, accurate, 31 

external, 27 

internal, 27 
Odors, classification of, 53 
Olfaction, 53 ff. 

Organism a social group, 20, 21, 170 ff. 
Overtones, 84 



Palmesthesis, 99-101 
P'arachromopsia, 75 ff. 
Paradoxical cold, 99 
Parallax, 267 



Paralysis of the insane, general, 351-2 

Paranoia, 350 

Paraphrenia, 349 

Paresis, 351 2 

Parosphresia, 56 

Parsimony, law of, 30, 117 

Partials, 84 ff. 

Pathos, 317 

Pavloff 's experiment, 211, 303 

Perception, 156-7 

and language, 243-4 

auditory space, 277-80 

conditions of accurate, 232 ff. 

depth, 263 ff., 266-7 

development of, 239 ff. 

direct and indirect, 239 ff. 

integration in, 241 ff. 

objects of, 37 ff. 

of movement, 282 ff. 

olfactory space, 280-1 

space, 261 ff. 

symbolic, 254 ff., 263-276 

through imperceptible signs, 258-9 

visual anethesia in, 288-90 
Personality, 341 

alterations of, 343 
Perspective, aerial, 274-6 

angular, 272-3 

linear, 270-2 
Photometry, 139 ff. 

flicker, 140-1 
Photometer, Liimmer-Brodhum, 171 
Phobias, 355 
Phosphenes, 116 
Pitch, 80 ff. 

absolute, 151 

difference threshold, 150-1 
Pithiatism, 353-5 
Plagiarism, 162 
Pleasantness and unpleasantness, 111, 317, 

329 ff., 334, 338 9 
Plexus of Meissner and Auerbach, 179 
Poggendorf 's illusion, 292, 294-5 
Politzer's acumeter, 148 
Position, spatial, 118, 261 
Postganglionic neurons, 182 
Practice, 231-2, 234 

and nystagmus, 286 
Predisposition, 210 
Preganglionic neurons, 182 
Presbyopia, 135 
Prism experiment, 262 
Proof, scientific, 32 
Proprioception, 42, 101 
Protanope, 75 ff., 146-7 
Protensity, 39 
Protoplasm, 172 
Psychasthenia, 355 



INDEX 



367 



Psychology, abnormal, 15, 17, 345 ff. 

animal, 15, 17 

applied, 19 

as a science, 28 

behavioristic, 35, 332, 333 

child, 15, 16 

commercial and industrial, 18 

comparative, 18 

defined, 19, 23 

educational, 18 

experimental, 19 

genetic, 18, 33, 35, 331-3 

individual, 164-5 

introspectionalist, 33-34, 333 

methods of, 28 

of adolescence, 16 

pseudo, 32 

social, 15, 16, 329 

terms in, 22 
Psychoneuroses, 347 
Psychoses, 347, 348 ff. 
Pupillary reflex, 190 
Pain, 331 

cardiac, 107 

referred, 280-282 

sensitivity, 153 
Pain sense, the, 103 ff. 



Q 

Quality, 39, 112 

physiological conditions of, 115 
Questionary method, 165 ff. 



E 

Eange of color perception, 65 

of pitch perception, 83-4, 149 
Eeaction, 21, 48 

and consciousness, 202 ff. 

and discrimination, 244 ff. 

and feeling, 314 ff. 

reduction of, 188 

types of, 189 ff. 
Eeactions, 186 ff. 

automatic, 196-7, 307 

formation of, 230-5 

ideational, 193 

instinctive, 210, 214 ff. 

of glands and smooth muscle, 199 ff. 

perceptual, 192-3, 241 ff. 

serial connections of, 235 ff. 

thought, 298 ff. 

volitional, 194-6 
Reasoning, 308 ff. 
Eecency, 233 
Eeceptors, 48-49, 175, 178, 179, 186 

algetic, 104 



Eeceptors — Cont 'd. 

auditory, 90, 91, 119 

fatigue, 109 

of alimentary canal, 105 

of dermal senses, 95 

pain, 98 

sexual, 101 

visceral, 314 

visual, 62 
Eecognition, 161-162 
Eeflexes, 189 ff., 203, 205, 209 
Eelations, 122 ff. 

simple, 123 

space, 261 
Eelativity of sense data, 112 
Eelearning method, the, 230 
Eelief, 106 

Eeligion, psychology of, 18 
Eepugnanee, 325 
Eesponse, see reaction 
Eeward and punishment, 226 

S 

Saccadic eye movement, 288-90 

Satisfaction, 106 

Saturation, 39, 58, ff. 

Sarcoplasm, 172 

Scale, musical,. 86 ff. 

Science, principles of, 28 

Scientific method in observation, 253-4 

Self, double, 342-3 

Self, the empirical, 341 ff. 

Sensation, 32, 38, 116 

Sense, modes of, 40 

Senses, 40 ff. 

cranial, 50 ff. 

modal, 42 

regional, 41-42 
Sensitivity, alimentary, 105 

auditory, 148 

epicritic, 95-97 

hair, 98 

joint, 102 

kinesthetic, 154-5 

normal color, 66-7 

organic, 103, 116 

pain, 153-4 

pressure, 151, 152 

protopathic, 95-7 

sexual, 101 

thermal, 154 

visual, 135, 138, 139, 142 
Sensory centers, 184-5 
Sensory measurements, 131 
SentiendP, 38 

auditory, 80 

bodilv, 314 






368 



INDEX 



Sentienda — Cont 'd. 

character of, 39 

gustatory, 50 

olfactory, 53 

relativity of, 112 

visual, 56 
Sentiments, 321 
Sex desire, 324, 328-9 
Sex excitement, 201, 317 
Sex feelings and habit, 338 
Sex, psychology of, 18 
Sexual sensitivity, 101 
Snellen's letters, 137 
Synapses, 178 
Social organization, 171 
Soul, 19 
Space perception, 261 ff. 

auditory, 277-80 

olfactory and organic, 280-2 
Spatial illusion, 291 ff. 
Spectrum, the, 63 ff. 
Spontaneous activities, 198 
Steroscopy, 267-8 
Stigmata, hysterical, 354 
Stilling 's, test, 145 
Stimulation, 21, 48 

inadequate, 178 

of temperature, 99 

vestibular and labyrinthine, 283-7 
Stimuli, 22, 43 ff. 

absoluteness of, 112-113 

auditory, 81 ff. 

gustatory, 51 

of fatigue, 110 
Stimuli, inadequate, 116 

olfactory, 53 

pain, 104, 106 

palmesthetic, 100 

thermal, 95, 97-98 

visual, 62 ff. 
Stimulus pattern, 189 
Stomach contractions in hunger, 336-7 
Strain and relaxation, 317 
Stratton 's experiment, 262 

illusion, 294 
Stroboscopic phenomena, 290-1 
Substance, 24 
Succession, 123 



Talbot-Plateau law, 141 
Test, cancellation, 231 

substitution, 231 
Tests of color vision, 143 ff. 

sensory, 131 ff. 
Terms, confusion in, 32 



Tetrahedron, taste, 50-51 
Thinking, 156, 193-4, 298 ff. 

symbolic, 164 
Thirst, 105 
Thought, 156 ff. 

and language, 303-4 
Threshold, difference, 124 ff. 

for brightness, 139 ff. ' 

for hue, 142-3 

for saturation, 143 

for touch, 153 
Threshold, stimulus, 113-115 
Tickle, 95-96 
Timber, 84 ff. 
Tissues, animal, 174 
Tobacco, and color blindness, 77 

and taste sensitivity, 52 
Tones, 80 
Tone-gaps, 91 
Transit, neural, 187 
Trial and error method, 233 
Triangle, color, 58-59 
Types of imagination, 157-8, 164 ff. 



U 



Universal, the, 163 



v 



Verbal style and imagery, 167 
Vertigo, 109, 286 
Vestibular sense, 108-109 
Viscera, sensitivity of, 41 
Visibile, minimal, 136-8 
Vision, 56 ff. 

central and peripheral, 74-5 

tests of color, 143 ff. 
Visual anesthesia, 288-90 
Visual acuity instrument, Cobb's, 138 
Vividness, 203 ff., 224 
Volition, 164 

and instinct, 219 ff. 
von Frey's esthesiometer, 151, 153 



W 

"Walking reflex, 199 

Wave lengths of light, 63, 65, 66 

Weber's law, 149, 125 ff. 

Will, 164 

Wilson's test, 144 



Zollner's illusion, 293, 295 



